diff --git a/DESCRIPTION b/DESCRIPTION
index 31a6de3..6c60f4a 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -1,7 +1,7 @@
 Package: trps
 Type: Package
-Title: Bayesian Trophic Position Models using 'stan'
-Version: 0.1.0
+Title: Bayesian Trophic Position Models using 'Stan'
+Version: 0.1.1
 Authors@R: c(
     person(
       "Benjamin L.", "Hlina",
@@ -23,7 +23,8 @@ Imports:
     brms,
     cli,
     dplyr,
-    lifecycle
+    lifecycle,
+    rlang
 Suggests: 
     bayesplot,
     ggdist,
@@ -37,7 +38,7 @@ Suggests:
     tidyr,
     viridis
 Config/testthat/edition: 3
-RoxygenNote: 7.3.2
+RoxygenNote: 7.3.3
 Roxygen: list(markdown = TRUE)
 Depends: 
     R (>= 4.1.0)
diff --git a/R/add_alpha.R b/R/add_alpha.R
index 37a0da0..60ebf00 100644
--- a/R/add_alpha.R
+++ b/R/add_alpha.R
@@ -32,36 +32,12 @@
 
 add_alpha <- function(
     data,
-    abs = FALSE) {
-  if (!(inherits(data, c(
-    "data.frame", "tibble",
-    "data.table"
-  )))) {
-    cli::cli_abort(c(
-      "`data` must be a data.frame, tibble, or data.table",
-      "i" = "Please provide data.frame"
-    ))
-  }
-
-  rv <- c("d13c", "c1", "c2")
-
-  if (!all(rv %in% names(data))) {
-    mv <- setdiff(rv, names(data))
-
-    cli::cli_abort(c(
-      "The data.frame is missing: {mv}",
-      "i" = "Please provide {mv}"
-    ))
-  }
-
+    abs = FALSE
+) {
 
-
-  if (!(is.logical(abs))) {
-    cli::cli_abort(c(
-      "`abs` argument must be a logical value",
-      "i" = "Please provide TRUE or FALSE"
-    ))
-  }
+  check_data_frame(data)
+  check_column_names(data)
+  check_logical(abs)
 
   if (isFALSE(abs)) {
     dat <- data |>
diff --git a/R/one_source_model.R b/R/one_source_model.R
index 2db6e50..f40490d 100644
--- a/R/one_source_model.R
+++ b/R/one_source_model.R
@@ -34,12 +34,7 @@
 #' @export
 
 one_source_model <- function(bp = FALSE) {
-  if (!(is.logical(bp))) {
-    cli::cli_abort(c(
-      "`bp` argument must be a logical value",
-      "i" = "Please provide TRUE or FALSE"
-    ))
-  }
+  check_logical(bp)
 
   if (isFALSE(bp)) {
     model <- brms::bf(
diff --git a/R/one_source_priors.R b/R/one_source_priors.R
index 41f38aa..268e3e4 100644
--- a/R/one_source_priors.R
+++ b/R/one_source_priors.R
@@ -18,13 +18,7 @@
 #' @export
 
 one_source_priors <- function(bp = FALSE) {
-  if (!(is.logical(bp))) {
-    cli::cli_abort(c(
-      "`bp` argument must be a logical value",
-      "i" = "Please provide TRUE or FALSE"
-    ))
-  }
-
+  check_logical(bp)
 
   if (isFALSE(bp)) {
     #  set priors
@@ -71,7 +65,5 @@ one_source_priors <- function(bp = FALSE) {
     )
   }
 
-
-
   return(priors)
 }
diff --git a/R/one_source_priors_params.R b/R/one_source_priors_params.R
index 531dbe2..247df01 100644
--- a/R/one_source_priors_params.R
+++ b/R/one_source_priors_params.R
@@ -55,145 +55,61 @@ one_source_priors_params <- function(
     sigma_lb = NULL,
     sigma_ub = NULL,
     bp = FALSE) {
-  if (!(is.logical(bp))) {
-    cli::cli_abort(c(
-      "`bp` argument must be a logical value",
-      "i" = "Please provide TRUE or FALSE"
-    ))
-  }
-
-  # ----- n1 -----
-
-  # set n1 to 9
-  if (is.null(n1)) {
-    n1 <- 9
-  }
-
-  # create error message for n1 priros
-  if (!is.numeric(n1)) {
-    cli::cli_abort(c(
-      "`n1` argument must be a numerical value.",
-      "i" = "Please provide a numerical value as a piror."
-    ))
-  }
-
-  # set n1_sigma to 1
-  if (is.null(n1_sigma)) {
-    n1_sigma <- 1
-  }
-  # create error message for n1 priors
-  if (!is.numeric(n1_sigma)) {
-    cli::cli_abort(c(
-      "`n1_sigma` argument must be a numerical value",
-      "i" = "Please provide a numerical value as a piror"
-    ))
-  }
-  # create error message for dn priros
-
-
-  if (is.null(dn)) {
-    dn <- 3.4
-  }
-
-  if (!is.numeric(dn)) {
-    cli::cli_abort(c(
-      "`dn` argument must be a numerical value",
-      "i" = "Please provide a numerical value as a pirorr"
-    ))
-  }
-
-  # create error message for dn priors
-  if (is.null(dn_sigma)) {
-    dn_sigma <- 0.25
-  }
 
-  if (!is.numeric(dn_sigma)) {
-    cli::cli_abort(c(
-      "`dn_sigma` argument must be a numerical value",
-      "i" = "Please provide a numerical value as a piror"
-    ))
-  }
-
-  # ----- tp -----
-
-  # set piror for tp
-  if (is.null(tp_lb)) {
-    tp_lb <- 2
-  }
+  check_logical(bp)
 
-  # create error message for tp priros
+  # ---- defualt values
 
-  if (!is.numeric(tp_lb)) {
-    cli::cli_abort(c(
-      "`tp_lb` argument must be a numerical value",
-      "i" = "Please provide a numerical value as a piror"
-    ))
-  }
-
-  if (is.null(tp_ub)) {
-    tp_ub <- 10
-  }
+  defaults <- default_priors("one_source")
 
-  # create error message for n1 priors
-  if (!is.numeric(tp_ub)) {
-    cli::cli_abort(c(
-      "`tp_ub` argument must be a numerical value",
-      "i" = "Please provide a numerical value as a piror"
-    ))
-  }
-  # ----- sigma -----
+  # supplied <- supplied_priors("one_source")
+  supplied <- list(
+    n1 = n1,
+    n1_sigma = n1_sigma,
+    dn = dn,
+    dn_sigma = dn_sigma,
+    tp_lb = tp_lb,
+    tp_ub = tp_ub,
+    sigma_lb = sigma_lb,
+    sigma_ub = sigma_ub
+  )
 
-  # set piror for tp
-  if (is.null(sigma_lb)) {
-    sigma_lb <- 0
-  }
 
-  # create error message for tp priros
+  params <- Map(function(x, d) if (is.null(x)) d else x, supplied, defaults)
 
-  if (!is.numeric(sigma_lb)) {
-    cli::cli_abort(c(
-      "`sigma_lb` argument must be a numerical value",
-      "i" = "Please provide a numerical value as a piror"
-    ))
-  }
+  lapply(names(params), function(nm) {
+    check_numerical(params[[nm]], arg_name = nm)
+  })
 
-  if (is.null(sigma_ub)) {
-    sigma_ub <- 10
-  }
+  params_env <- list2env(params, parent = environment())
 
-  # create error message for n1 priors
-  if (!is.numeric(sigma_ub)) {
-    cli::cli_abort(c(
-      "`sigma_ub` argument must be a numerical value",
-      "i" = "Please provide a numerical value as a piror"
-    ))
-  }
+  # ---- set prior
+  priors_params <- if (isTRUE(bp)) {
+    with(params_env, {
 
+      brms::stanvar(n1, name = "n1") +
+        brms::stanvar(n1_sigma, "n1_sigma") +
+        brms::stanvar(dn, "dn") +
+        brms::stanvar(dn_sigma, "dn_sigma") +
+        brms::stanvar(tp_lb, "tp_lb") +
+        brms::stanvar(tp_ub, "tp_ub") +
+        brms::stanvar(sigma_lb, "sigma_lb") +
+        brms::stanvar(sigma_ub, "sigma_ub")
+    }
+    )
+  } else {
 
-  if (isTRUE(bp)) {
-    priors_params <- brms::stanvar(n1, name = "n1") +
-      brms::stanvar(n1_sigma, "n1_sigma") +
+    with(params_env, {
       brms::stanvar(dn, "dn") +
-      brms::stanvar(dn_sigma, "dn_sigma") +
-      brms::stanvar(tp_lb, "tp_lb") +
-      brms::stanvar(tp_ub, "tp_ub") +
-      brms::stanvar(sigma_lb, "sigma_lb") +
-      brms::stanvar(sigma_ub, "sigma_ub")
+        brms::stanvar(dn_sigma, "dn_sigma") +
+        brms::stanvar(tp_lb, "tp_lb") +
+        brms::stanvar(tp_ub, "tp_ub") +
+        brms::stanvar(sigma_lb, "sigma_lb") +
+        brms::stanvar(sigma_ub, "sigma_ub")
+    }
+    )
   }
 
 
-  # ----- dn -----
-
-  if (isFALSE(bp)) {
-    # ----- set prirors -----
-
-    priors_params <- brms::stanvar(dn, "dn") +
-      brms::stanvar(dn_sigma, "dn_sigma") +
-      brms::stanvar(tp_lb, "tp_lb") +
-      brms::stanvar(tp_ub, "tp_ub") +
-      brms::stanvar(sigma_lb, "sigma_lb") +
-      brms::stanvar(sigma_ub, "sigma_ub")
-  }
-
   return(priors_params)
 }
diff --git a/R/two_source_model.R b/R/two_source_model.R
index 1a6074b..abea3b3 100644
--- a/R/two_source_model.R
+++ b/R/two_source_model.R
@@ -63,23 +63,15 @@
 
 two_source_model <- function(bp = FALSE,
                              lambda = NULL) {
-  if (!(is.logical(bp))) {
-    cli::cli_abort(c(
-      "`bp` argument must be a logical value",
-      "i" = "Please provide TRUE or FALSE"
-    ))
-  }
+
+
+  check_logical(bp)
 
   if (is.null(lambda)) {
     lambda <- 1
   }
 
-  if (!(is.numeric(lambda)) || !(lambda %in% c(1, 2))) {
-    cli::cli_abort(c(
-      "`lambda` argument must be a numeric value and either `1` or `2`",
-      "i" = "Please provide `1` or `2`"
-    ))
-  }
+  check_lambda(lambda)
 
   if (lambda == 1) {
     if (isFALSE(bp)) {
diff --git a/R/two_source_model_ar.R b/R/two_source_model_ar.R
index 9de3c9f..0f2ea5f 100644
--- a/R/two_source_model_ar.R
+++ b/R/two_source_model_ar.R
@@ -82,24 +82,14 @@
 two_source_model_ar <- function(
     bp = FALSE,
     lambda = NULL) {
-  if (!(is.logical(bp))) {
-    cli::cli_abort(c(
-      "`bp` argument must be a logical value",
-      "i" = "Please provide TRUE or FALSE"
-    ))
-  }
+
+  check_logical(bp)
 
   if (is.null(lambda)) {
     lambda <- 1
   }
 
-  if (!(is.numeric(lambda)) || !(lambda %in% c(1, 2))) {
-    cli::cli_abort(c(
-      "`lambda` argument must be a numeric value and either `1` or `2`",
-      "i" = "Please provide `1` or `2`"
-    ))
-  }
-
+  check_lambda(lambda)
   # ---- singe lambda ----
   if (lambda == 1) {
     # ---- no baseline priors -----
diff --git a/R/two_source_model_arc.R b/R/two_source_model_arc.R
index 311ee09..5787f18 100644
--- a/R/two_source_model_arc.R
+++ b/R/two_source_model_arc.R
@@ -84,23 +84,14 @@
 two_source_model_arc <- function(
     bp = FALSE,
     lambda = NULL) {
-  if (!(is.logical(bp))) {
-    cli::cli_abort(c(
-      "`bp` argument must be a logical value",
-      "i" = "Please provide TRUE or FALSE"
-    ))
-  }
+
+  check_logical(bp)
 
   if (is.null(lambda)) {
     lambda <- 1
   }
 
-  if (!(is.numeric(lambda)) || !(lambda %in% c(1, 2))) {
-    cli::cli_abort(c(
-      "`lambda` argument must be a numeric value and either `1` or `2`",
-      "i" = "Please provide `1` or `2`"
-    ))
-  }
+  check_lambda(lambda)
 
   # ---- singe lambda ----
   if (lambda == 1) {
diff --git a/R/two_source_priors.R b/R/two_source_priors.R
index fd2d02a..b7c5489 100644
--- a/R/two_source_priors.R
+++ b/R/two_source_priors.R
@@ -20,13 +20,8 @@
 #' @export
 
 two_source_priors <- function(bp = FALSE) {
-  if (!(is.logical(bp))) {
-    cli::cli_abort(c(
-      "`bp` argument must be a logical value",
-      "i" = "Please provide TRUE or FALSE"
-    ))
-  }
 
+  check_logical(bp)
 
   if (isFALSE(bp)) {
     #  set priors
diff --git a/R/two_source_priors_ar.R b/R/two_source_priors_ar.R
index 5a07572..d76a41f 100644
--- a/R/two_source_priors_ar.R
+++ b/R/two_source_priors_ar.R
@@ -21,12 +21,7 @@
 #' @export
 
 two_source_priors_ar <- function(bp = FALSE) {
-  if (!(is.logical(bp))) {
-    cli::cli_abort(c(
-      "`bp` argument must be a logical value",
-      "i" = "Please provide TRUE or FALSE"
-    ))
-  }
+  check_logical(bp)
 
 
   if (isFALSE(bp)) {
@@ -41,17 +36,17 @@ two_source_priors_ar <- function(bp = FALSE) {
       brms::prior(normal(dn, dn_sigma), resp = "d15n", nlpar = "dn"),
       # Trophic Position (tp)
       brms::prior(uniform(tp_lb, tp_ub),
-        lb = tp_lb, ub = tp_ub, resp = "d15n",
-        nlpar = "tp"
+                  lb = tp_lb, ub = tp_ub, resp = "d15n",
+                  nlpar = "tp"
       ),
       # Standard deviation prior
       brms::prior(uniform(sigma_lb, sigma_ub),
-        resp = "alpha",
-        class = "sigma", ub = sigma_ub
+                  resp = "alpha",
+                  class = "sigma", ub = sigma_ub
       ),
       brms::prior(uniform(sigma_lb, sigma_ub),
-        resp = "d15n",
-        class = "sigma", ub = sigma_ub
+                  resp = "d15n",
+                  class = "sigma", ub = sigma_ub
       )
     )
   }
@@ -66,29 +61,29 @@ two_source_priors_ar <- function(bp = FALSE) {
 
       # Baseline 1 δ15N (n1)
       brms::prior(normal(n1, n1_sigma),
-        resp = "d15n",
-        nlpar = "n1"
+                  resp = "d15n",
+                  nlpar = "n1"
       ),
       # Baseline 2 δ15N (n2)
       brms::prior(normal(n2, n2_sigma),
-        resp = "d15n",
-        nlpar = "n2"
+                  resp = "d15n",
+                  nlpar = "n2"
       ),
       # Trophic enrichment factor (ΔN)
       brms::prior(normal(dn, dn_sigma), resp = "d15n", nlpar = "dn"),
       # Trophic Position (tp)
       brms::prior(uniform(tp_lb, tp_ub),
-        lb = tp_lb, ub = tp_ub, resp = "d15n",
-        nlpar = "tp"
+                  lb = tp_lb, ub = tp_ub, resp = "d15n",
+                  nlpar = "tp"
       ),
       # Standard deviation prior
       brms::prior(uniform(sigma_lb, sigma_ub),
-        resp = "alpha",
-        class = "sigma", ub = sigma_ub
+                  resp = "alpha",
+                  class = "sigma", ub = sigma_ub
       ),
       brms::prior(uniform(sigma_lb, sigma_ub),
-        resp = "d15n",
-        class = "sigma", ub = sigma_ub
+                  resp = "d15n",
+                  class = "sigma", ub = sigma_ub
       )
     )
   }
diff --git a/R/two_source_priors_arc.R b/R/two_source_priors_arc.R
index d548f87..d8580c1 100644
--- a/R/two_source_priors_arc.R
+++ b/R/two_source_priors_arc.R
@@ -21,12 +21,8 @@
 #' @export
 
 two_source_priors_arc <- function(bp = FALSE) {
-  if (!(is.logical(bp))) {
-    cli::cli_abort(c(
-      "`bp` argument must be a logical value",
-      "i" = "Please provide TRUE or FALSE"
-    ))
-  }
+
+  check_logical(bp)
 
 
   if (isFALSE(bp)) {
diff --git a/R/two_source_priors_params.R b/R/two_source_priors_params.R
index fa665ba..3b8093c 100644
--- a/R/two_source_priors_params.R
+++ b/R/two_source_priors_params.R
@@ -100,261 +100,75 @@ two_source_priors_params <- function(
     sigma_lb = NULL,
     sigma_ub = NULL,
     bp = FALSE) {
-  if (!(is.logical(bp))) {
-    cli::cli_abort(c(
-      "`bp` argument must be a logical value",
-      "i" = "Please provide TRUE or FALSE"
-    ))
-  }
-
-  # ----- a -----
-
-  # set a to 1
-  if (is.null(a)) {
-    a <- 1
-  }
-
-  # create error message for a priros
-  if (!is.numeric(a)) {
-    cli::cli_abort(c(
-      "`a` argument must be a numerical value.",
-      "i" = "Please provide a numerical value as a piror."
-    ))
-  }
-
-  # set b to 1
-  if (is.null(b)) {
-    b <- 1
-  }
-  # create error message for b priors
-  if (!is.numeric(b)) {
-    cli::cli_abort(c(
-      "`b` argument must be a numerical value",
-      "i" = "Please provide a numerical value as a piror"
-    ))
-  }
-
-  # ----- c1 -----
-
-  # set c1 to 21
-  if (is.null(c1)) {
-    c1 <- -21
-  }
-
-  # create error message for n1 priros
-  if (!is.numeric(c1)) {
-    cli::cli_abort(c(
-      "`c1` argument must be a numerical value.",
-      "i" = "Please provide a numerical value as a piror."
-    ))
-  }
-
-  # set c1_sigma to 1
-  if (is.null(c1_sigma)) {
-    c1_sigma <- 1
-  }
-  # create error message for c1 priors
-  if (!is.numeric(c1_sigma)) {
-    cli::cli_abort(c(
-      "`c1_sigma` argument must be a numerical value",
-      "i" = "Please provide a numerical value as a piror"
-    ))
-  }
-  # ----- c2 -----
-
-  # set c2 to -25
-  if (is.null(c2)) {
-    c2 <- -26
-  }
-
-  # create error message for n1 priros
-  if (!is.numeric(c2)) {
-    cli::cli_abort(c(
-      "`c2` argument must be a numerical value.",
-      "i" = "Please provide a numerical value as a piror."
-    ))
-  }
-
-  # set c1_sigma to 1
-  if (is.null(c2_sigma)) {
-    c2_sigma <- 1
-  }
-  # create error message for c1 priors
-  if (!is.numeric(c2_sigma)) {
-    cli::cli_abort(c(
-      "`c2_sigma` argument must be a numerical value",
-      "i" = "Please provide a numerical value as a piror"
-    ))
-  }
-  # ----- n1 -----
-
-  # set n1 to 9
-  if (is.null(n1)) {
-    n1 <- 8
-  }
-
-  # create error message for n1 priros
-  if (!is.numeric(n1)) {
-    cli::cli_abort(c(
-      "`n1` argument must be a numerical value.",
-      "i" = "Please provide a numerical value as a piror."
-    ))
-  }
-
-  # set n1_sigma to 1
-  if (is.null(n1_sigma)) {
-    n1_sigma <- 1
-  }
-  # create error message for n1 priors
-  if (!is.numeric(n1_sigma)) {
-    cli::cli_abort(c(
-      "`n1_sigma` argument must be a numerical value",
-      "i" = "Please provide a numerical value as a piror"
-    ))
-  }
-  # ----- n2 -----
-
-  # set n1 to 9
-  if (is.null(n2)) {
-    n2 <- 9.5
-  }
-
-  # create error message for n1 priros
-  if (!is.numeric(n2)) {
-    cli::cli_abort(c(
-      "`n2` argument must be a numerical value.",
-      "i" = "Please provide a numerical value as a piror."
-    ))
-  }
-
-  # set n1_sigma to 1
-  if (is.null(n2_sigma)) {
-    n2_sigma <- 1
-  }
-  # create error message for n1 priors
-  if (!is.numeric(n2_sigma)) {
-    cli::cli_abort(c(
-      "`n2_sigma` argument must be a numerical value",
-      "i" = "Please provide a numerical value as a piror"
-    ))
-  }
-  # create error message for dn priros
-
-
-  if (is.null(dn)) {
-    dn <- 3.4
-  }
-
-  if (!is.numeric(dn)) {
-    cli::cli_abort(c(
-      "`dn` argument must be a numerical value",
-      "i" = "Please provide a numerical value as a pirorr"
-    ))
-  }
-
-  # create error message for dn priors
-  if (is.null(dn_sigma)) {
-    dn_sigma <- 0.25
-  }
-
-  if (!is.numeric(dn_sigma)) {
-    cli::cli_abort(c(
-      "`dn_sigma` argument must be a numerical value",
-      "i" = "Please provide a numerical value as a piror"
-    ))
-  }
-
-  # ----- tp -----
-
-  # set piror for tp
-  if (is.null(tp_lb)) {
-    tp_lb <- 2
-  }
-
-  # create error message for tp priros
-
-  if (!is.numeric(tp_lb)) {
-    cli::cli_abort(c(
-      "`tp_lb` argument must be a numerical value",
-      "i" = "Please provide a numerical value as a piror"
-    ))
-  }
-
-  if (is.null(tp_ub)) {
-    tp_ub <- 10
-  }
-
-  # create error message for n1 priors
-  if (!is.numeric(tp_ub)) {
-    cli::cli_abort(c(
-      "`tp_ub` argument must be a numerical value",
-      "i" = "Please provide a numerical value as a piror"
-    ))
-  }
-  # ----- sigma -----
-
-  # set piror for tp
-  if (is.null(sigma_lb)) {
-    sigma_lb <- 0
-  }
-
-  # create error message for tp priros
-
-  if (!is.numeric(sigma_lb)) {
-    cli::cli_abort(c(
-      "`sigma_lb` argument must be a numerical value",
-      "i" = "Please provide a numerical value as a piror"
-    ))
-  }
-
-  if (is.null(sigma_ub)) {
-    sigma_ub <- 10
-  }
-
-  # create error message for n1 priors
-  if (!is.numeric(sigma_ub)) {
-    cli::cli_abort(c(
-      "`sigma_ub` argument must be a numerical value",
-      "i" = "Please provide a numerical value as a piror"
-    ))
-  }
 
-
-  if (isTRUE(bp)) {
-    priors_params <-
+  check_logical(bp)
+  # set defualts
+  defaults <- default_priors("two_source")
+
+  # ---- suplied
+  supplied <- list(
+    a = a,
+    b = b,
+    c1 = c1,
+    c1_sigma = c1_sigma,
+    c2 = c2,
+    c2_sigma = c2_sigma,
+    n1 = n1,
+    n1_sigma = n1_sigma,
+    n2 = n2,
+    n2_sigma = n2_sigma,
+    dn = dn,
+    dn_sigma = dn_sigma,
+    tp_lb = tp_lb,
+    tp_ub = tp_ub,
+    sigma_lb = sigma_lb,
+    sigma_ub = sigma_ub
+  )
+
+  # ---- either set defaults or supplied ------
+  params <- Map(function(x, d) if (is.null(x)) d else x, supplied, defaults)
+
+  # check them
+  lapply(names(params), function(nm) {
+    check_numerical(params[[nm]], arg_name = nm)
+  })
+  # ----- put them in to function envo
+  params_env <- list2env(params, parent = environment())
+
+
+
+  priors_params <- if (isTRUE(bp)) {
+    with(params_env, {
       brms::stanvar(a, name = "a") +
-      brms::stanvar(b, "b") +
-      brms::stanvar(c1, name = "c1") +
-      brms::stanvar(c1_sigma, "c1_sigma") +
-      brms::stanvar(c2, name = "c2") +
-      brms::stanvar(c2_sigma, "c2_sigma") +
-      brms::stanvar(n1, name = "n1") +
-      brms::stanvar(n1_sigma, "n1_sigma") +
-      brms::stanvar(n2, name = "n2") +
-      brms::stanvar(n2_sigma, "n2_sigma") +
-      brms::stanvar(dn, "dn") +
-      brms::stanvar(dn_sigma, "dn_sigma") +
-      brms::stanvar(tp_lb, "tp_lb") +
-      brms::stanvar(tp_ub, "tp_ub") +
-      brms::stanvar(sigma_lb, "sigma_lb") +
-      brms::stanvar(sigma_ub, "sigma_ub")
-  }
-
-
-  # ----- dn -----
-
-  if (isFALSE(bp)) {
-    # ----- set prirors -----
-
-    priors_params <-
+        brms::stanvar(b, "b") +
+        brms::stanvar(c1, name = "c1") +
+        brms::stanvar(c1_sigma, "c1_sigma") +
+        brms::stanvar(c2, name = "c2") +
+        brms::stanvar(c2_sigma, "c2_sigma") +
+        brms::stanvar(n1, name = "n1") +
+        brms::stanvar(n1_sigma, "n1_sigma") +
+        brms::stanvar(n2, name = "n2") +
+        brms::stanvar(n2_sigma, "n2_sigma") +
+        brms::stanvar(dn, "dn") +
+        brms::stanvar(dn_sigma, "dn_sigma") +
+        brms::stanvar(tp_lb, "tp_lb") +
+        brms::stanvar(tp_ub, "tp_ub") +
+        brms::stanvar(sigma_lb, "sigma_lb") +
+        brms::stanvar(sigma_ub, "sigma_ub")
+    }
+    )
+  } else {
+    with(params_env, {
       brms::stanvar(a, name = "a") +
-      brms::stanvar(b, "b") +
-      brms::stanvar(dn, "dn") +
-      brms::stanvar(dn_sigma, "dn_sigma") +
-      brms::stanvar(tp_lb, "tp_lb") +
-      brms::stanvar(tp_ub, "tp_ub") +
-      brms::stanvar(sigma_lb, "sigma_lb") +
-      brms::stanvar(sigma_ub, "sigma_ub")
+        brms::stanvar(b, "b") +
+        brms::stanvar(dn, "dn") +
+        brms::stanvar(dn_sigma, "dn_sigma") +
+        brms::stanvar(tp_lb, "tp_lb") +
+        brms::stanvar(tp_ub, "tp_ub") +
+        brms::stanvar(sigma_lb, "sigma_lb") +
+        brms::stanvar(sigma_ub, "sigma_ub")
+    }
+    )
   }
 
   return(priors_params)
diff --git a/R/two_source_priors_params_ar.R b/R/two_source_priors_params_ar.R
index 386f7f6..6674141 100644
--- a/R/two_source_priors_params_ar.R
+++ b/R/two_source_priors_params_ar.R
@@ -119,205 +119,68 @@ two_source_priors_params_ar <- function(
     sigma_lb = NULL,
     sigma_ub = NULL,
     bp = FALSE) {
-  if (!(is.logical(bp))) {
-    cli::cli_abort(c(
-      "`bp` argument must be a logical value",
-      "i" = "Please provide TRUE or FALSE"
-    ))
-  }
-
-  # ----- a -----
-
-  # set a to 1
-  if (is.null(a)) {
-    a <- 1
-  }
-
-  # create error message for a priros
-  if (!is.numeric(a)) {
-    cli::cli_abort(c(
-      "`a` argument must be a numerical value.",
-      "i" = "Please provide a numerical value as a piror."
-    ))
-  }
-
-  # set b to 1
-  if (is.null(b)) {
-    b <- 1
-  }
-  # create error message for b priors
-  if (!is.numeric(b)) {
-    cli::cli_abort(c(
-      "`b` argument must be a numerical value",
-      "i" = "Please provide a numerical value as a piror"
-    ))
-  }
-
-  # ----- n1 -----
-
-  # set n1 to 9
-  if (is.null(n1)) {
-    n1 <- 8.0
-  }
-
-  # create error message for n1 priros
-  if (!is.numeric(n1)) {
-    cli::cli_abort(c(
-      "`n1` argument must be a numerical value.",
-      "i" = "Please provide a numerical value as a piror."
-    ))
-  }
-
-  # set n1_sigma to 1
-  if (is.null(n1_sigma)) {
-    n1_sigma <- 1
-  }
-  # create error message for n1 priors
-  if (!is.numeric(n1_sigma)) {
-    cli::cli_abort(c(
-      "`n1_sigma` argument must be a numerical value",
-      "i" = "Please provide a numerical value as a piror"
-    ))
-  }
-  # ----- n2 -----
-
-  # set n1 to 9
-  if (is.null(n2)) {
-    n2 <- 9.5
-  }
-
-  # create error message for n1 priros
-  if (!is.numeric(n2)) {
-    cli::cli_abort(c(
-      "`n2` argument must be a numerical value.",
-      "i" = "Please provide a numerical value as a piror."
-    ))
-  }
-
-  # set n1_sigma to 1
-  if (is.null(n2_sigma)) {
-    n2_sigma <- 1
-  }
-  # create error message for n1 priors
-  if (!is.numeric(n2_sigma)) {
-    cli::cli_abort(c(
-      "`n2_sigma` argument must be a numerical value",
-      "i" = "Please provide a numerical value as a piror"
-    ))
-  }
-  # ---- dn priors -----
-
-
-  if (is.null(dn)) {
-    dn <- 3.4
-  }
-
-  if (!is.numeric(dn)) {
-    cli::cli_abort(c(
-      "`dn` argument must be a numerical value",
-      "i" = "Please provide a numerical value as a pirorr"
-    ))
-  }
 
-  # create error message for dn priors
-  if (is.null(dn_sigma)) {
-    dn_sigma <- 0.25
-  }
-
-  if (!is.numeric(dn_sigma)) {
-    cli::cli_abort(c(
-      "`dn_sigma` argument must be a numerical value",
-      "i" = "Please provide a numerical value as a piror"
-    ))
-  }
-
-  # ----- tp -----
-
-  # set piror for tp
-  if (is.null(tp_lb)) {
-    tp_lb <- 2
-  }
-
-  # create error message for tp priros
-
-  if (!is.numeric(tp_lb)) {
-    cli::cli_abort(c(
-      "`tp_lb` argument must be a numerical value",
-      "i" = "Please provide a numerical value as a piror"
-    ))
-  }
-
-  if (is.null(tp_ub)) {
-    tp_ub <- 10
-  }
-
-  # create error message for n1 priors
-  if (!is.numeric(tp_ub)) {
-    cli::cli_abort(c(
-      "`tp_ub` argument must be a numerical value",
-      "i" = "Please provide a numerical value as a piror"
-    ))
-  }
-  # ----- sigma -----
-
-  # set piror for tp
-  if (is.null(sigma_lb)) {
-    sigma_lb <- 0
-  }
-
-  # create error message for tp priros
-
-  if (!is.numeric(sigma_lb)) {
-    cli::cli_abort(c(
-      "`sigma_lb` argument must be a numerical value",
-      "i" = "Please provide a numerical value as a piror"
-    ))
-  }
-
-  if (is.null(sigma_ub)) {
-    sigma_ub <- 10
-  }
-
-  # create error message for n1 priors
-  if (!is.numeric(sigma_ub)) {
-    cli::cli_abort(c(
-      "`sigma_ub` argument must be a numerical value",
-      "i" = "Please provide a numerical value as a piror"
-    ))
-  }
-
-
-  if (isTRUE(bp)) {
-    priors_params <-
+  check_logical(bp)
+
+  # ----- set defaults -----
+  defaults <- default_priors("two_source_ar")
+
+
+  # ---- suplied -----
+  supplied <- list(
+    a = a,
+    b = b,
+    n1 = n1,
+    n1_sigma = n1_sigma,
+    n2 = n2,
+    n2_sigma = n2_sigma,
+    dn = dn,
+    dn_sigma = dn_sigma,
+    tp_lb = tp_lb,
+    tp_ub = tp_ub,
+    sigma_lb = sigma_lb,
+    sigma_ub = sigma_ub
+  )
+
+
+  # ---- either set defaults or supplied ------
+  params <- Map(function(x, d) if (is.null(x)) d else x, supplied, defaults)
+
+  # check them
+  lapply(names(params), function(nm) {
+    check_numerical(params[[nm]], arg_name = nm)
+  })
+  # ----- put them in to function envo
+  params_env <- list2env(params, parent = environment())
+
+  priors_params <- if (isTRUE(bp)) {
+    with(params_env, {
       brms::stanvar(a, name = "a") +
-      brms::stanvar(b, "b") +
-      brms::stanvar(n1, name = "n1") +
-      brms::stanvar(n1_sigma, "n1_sigma") +
-      brms::stanvar(n2, name = "n2") +
-      brms::stanvar(n2_sigma, "n2_sigma") +
-      brms::stanvar(dn, "dn") +
-      brms::stanvar(dn_sigma, "dn_sigma") +
-      brms::stanvar(tp_lb, "tp_lb") +
-      brms::stanvar(tp_ub, "tp_ub") +
-      brms::stanvar(sigma_lb, "sigma_lb") +
-      brms::stanvar(sigma_ub, "sigma_ub")
-  }
-
-
-  # ----- dn -----
-
-  if (isFALSE(bp)) {
-    # ----- set prirors -----
-
-    priors_params <-
+        brms::stanvar(b, "b") +
+        brms::stanvar(n1, name = "n1") +
+        brms::stanvar(n1_sigma, "n1_sigma") +
+        brms::stanvar(n2, name = "n2") +
+        brms::stanvar(n2_sigma, "n2_sigma") +
+        brms::stanvar(dn, "dn") +
+        brms::stanvar(dn_sigma, "dn_sigma") +
+        brms::stanvar(tp_lb, "tp_lb") +
+        brms::stanvar(tp_ub, "tp_ub") +
+        brms::stanvar(sigma_lb, "sigma_lb") +
+        brms::stanvar(sigma_ub, "sigma_ub")
+    }
+    )
+  } else {
+    with(params_env, {
       brms::stanvar(a, name = "a") +
-      brms::stanvar(b, "b") +
-      brms::stanvar(dn, "dn") +
-      brms::stanvar(dn_sigma, "dn_sigma") +
-      brms::stanvar(tp_lb, "tp_lb") +
-      brms::stanvar(tp_ub, "tp_ub") +
-      brms::stanvar(sigma_lb, "sigma_lb") +
-      brms::stanvar(sigma_ub, "sigma_ub")
+        brms::stanvar(b, "b") +
+        brms::stanvar(dn, "dn") +
+        brms::stanvar(dn_sigma, "dn_sigma") +
+        brms::stanvar(tp_lb, "tp_lb") +
+        brms::stanvar(tp_ub, "tp_ub") +
+        brms::stanvar(sigma_lb, "sigma_lb") +
+        brms::stanvar(sigma_ub, "sigma_ub")
+    }
+    )
   }
 
   return(priors_params)
diff --git a/R/two_source_priors_params_arc.R b/R/two_source_priors_params_arc.R
index 8cbc623..ac67419 100644
--- a/R/two_source_priors_params_arc.R
+++ b/R/two_source_priors_params_arc.R
@@ -138,230 +138,45 @@ two_source_priors_params_arc <- function(
     sigma_lb = NULL,
     sigma_ub = NULL,
     bp = FALSE) {
-  if (!(is.logical(bp))) {
-    cli::cli_abort(c(
-      "`bp` argument must be a logical value",
-      "i" = "Please provide TRUE or FALSE"
-    ))
-  }
+
+  check_logical(bp)
 
   # ----- a -----
 
   # set a to 1
-  if (is.null(a)) {
-    a <- 1
-  }
-
-  # create error message for a priros
-  if (!is.numeric(a)) {
-    cli::cli_abort(c(
-      "`a` argument must be a numerical value.",
-      "i" = "Please provide a numerical value as a piror."
-    ))
-  }
-
-  # set b to 1
-  if (is.null(b)) {
-    b <- 1
-  }
-  # create error message for b priors
-  if (!is.numeric(b)) {
-    cli::cli_abort(c(
-      "`b` argument must be a numerical value",
-      "i" = "Please provide a numerical value as a piror"
-    ))
-  }
-
-  # ----- n1 -----
-
-  # set n1 to 9
-  if (is.null(n1)) {
-    n1 <- 8.0
-  }
-
-  # create error message for n1 priros
-  if (!is.numeric(n1)) {
-    cli::cli_abort(c(
-      "`n1` argument must be a numerical value.",
-      "i" = "Please provide a numerical value as a piror."
-    ))
-  }
-
-  # set n1_sigma to 1
-  if (is.null(n1_sigma)) {
-    n1_sigma <- 1
-  }
-  # create error message for n1 priors
-  if (!is.numeric(n1_sigma)) {
-    cli::cli_abort(c(
-      "`n1_sigma` argument must be a numerical value",
-      "i" = "Please provide a numerical value as a piror"
-    ))
-  }
-  # ----- n2 -----
-
-  # set n1 to 9
-  if (is.null(n2)) {
-    n2 <- 9.5
-  }
-
-  # create error message for n1 priros
-  if (!is.numeric(n2)) {
-    cli::cli_abort(c(
-      "`n2` argument must be a numerical value.",
-      "i" = "Please provide a numerical value as a piror."
-    ))
-  }
-
-  # set n1_sigma to 1
-  if (is.null(n2_sigma)) {
-    n2_sigma <- 1
-  }
-  # create error message for n1 priors
-  if (!is.numeric(n2_sigma)) {
-    cli::cli_abort(c(
-      "`n2_sigma` argument must be a numerical value",
-      "i" = "Please provide a numerical value as a piror"
-    ))
-  }
-  # ----- c1 -----
-
-  # set c1 to -21
-  if (is.null(c1)) {
-    c1 <- -21
-  }
-
-  # create error message for c1 priros
-  if (!is.numeric(c1)) {
-    cli::cli_abort(c(
-      "`c1` argument must be a numerical value.",
-      "i" = "Please provide a numerical value as a piror."
-    ))
-  }
-
-  # set c1_sigma to 1
-  if (is.null(c1_sigma)) {
-    c1_sigma <- 1
-  }
-  # create error message for n1 priors
-  if (!is.numeric(c1_sigma)) {
-    cli::cli_abort(c(
-      "`c1_sigma` argument must be a numerical value",
-      "i" = "Please provide a numerical value as a piror"
-    ))
-  }
-
-  # ----- c2 -----
-
-  # set c2 to -26
-  if (is.null(c2)) {
-    c2 <- -26
-  }
-
-  # create error message for c1 priros
-  if (!is.numeric(c2)) {
-    cli::cli_abort(c(
-      "`c2` argument must be a numerical value.",
-      "i" = "Please provide a numerical value as a piror."
-    ))
-  }
-
-  # set c1_sigma to 1
-  if (is.null(c2_sigma)) {
-    c2_sigma <- 1
-  }
-  # create error message for n1 priors
-  if (!is.numeric(c2_sigma)) {
-    cli::cli_abort(c(
-      "`c2_sigma` argument must be a numerical value",
-      "i" = "Please provide a numerical value as a piror"
-    ))
-  }
-
-  # ---- dn priors -----
-
-
-  if (is.null(dn)) {
-    dn <- 3.4
-  }
-
-  if (!is.numeric(dn)) {
-    cli::cli_abort(c(
-      "`dn` argument must be a numerical value",
-      "i" = "Please provide a numerical value as a pirorr"
-    ))
-  }
-
-  # create error message for dn priors
-  if (is.null(dn_sigma)) {
-    dn_sigma <- 0.25
-  }
-
-  if (!is.numeric(dn_sigma)) {
-    cli::cli_abort(c(
-      "`dn_sigma` argument must be a numerical value",
-      "i" = "Please provide a numerical value as a piror"
-    ))
-  }
-
-  # ----- tp -----
-
-  # set piror for tp
-  if (is.null(tp_lb)) {
-    tp_lb <- 2
-  }
-
-  # create error message for tp priros
-
-  if (!is.numeric(tp_lb)) {
-    cli::cli_abort(c(
-      "`tp_lb` argument must be a numerical value",
-      "i" = "Please provide a numerical value as a piror"
-    ))
-  }
-
-  if (is.null(tp_ub)) {
-    tp_ub <- 10
-  }
-
-  # create error message for n1 priors
-  if (!is.numeric(tp_ub)) {
-    cli::cli_abort(c(
-      "`tp_ub` argument must be a numerical value",
-      "i" = "Please provide a numerical value as a piror"
-    ))
-  }
-  # ----- sigma -----
-
-  # set piror for tp
-  if (is.null(sigma_lb)) {
-    sigma_lb <- 0
-  }
-
-  # create error message for tp priros
-
-  if (!is.numeric(sigma_lb)) {
-    cli::cli_abort(c(
-      "`sigma_lb` argument must be a numerical value",
-      "i" = "Please provide a numerical value as a piror"
-    ))
-  }
-
-  if (is.null(sigma_ub)) {
-    sigma_ub <- 10
-  }
-
-  # create error message for n1 priors
-  if (!is.numeric(sigma_ub)) {
-    cli::cli_abort(c(
-      "`sigma_ub` argument must be a numerical value",
-      "i" = "Please provide a numerical value as a piror"
-    ))
-  }
-
-
-  if (isTRUE(bp)) {
-    priors_params <-
+  defaults <- default_priors("two_source_arc")
+  # supplied
+  supplied <- list(
+    a = a,
+    b = b,
+    n1 = n1,
+    n1_sigma = n1_sigma,
+    n2 = n2,
+    n2_sigma = n2_sigma,
+    c1 = c1,
+    c1_sigma = c1_sigma,
+    c2 = c2,
+    c2_sigma = c2_sigma,
+    dn = dn,
+    dn_sigma = dn_sigma,
+    tp_lb = tp_lb,
+    tp_ub = tp_ub,
+    sigma_lb = sigma_lb,
+    sigma_ub = sigma_ub
+  )
+
+  # ---- either set defaults or supplied ------
+  params <- Map(function(x, d) if (is.null(x)) d else x, supplied, defaults)
+
+  # check them
+  lapply(names(params), function(nm) {
+    check_numerical(params[[nm]], arg_name = nm)
+  })
+  # ----- put them in to function envo
+  params_env <- list2env(params, parent = environment())
+
+  priors_params <- if (isTRUE(bp)) {
+    with(params_env, {
       brms::stanvar(a, name = "a") +
       brms::stanvar(b, "b") +
       brms::stanvar(n1, name = "n1") +
@@ -378,15 +193,10 @@ two_source_priors_params_arc <- function(
       brms::stanvar(tp_ub, "tp_ub") +
       brms::stanvar(sigma_lb, "sigma_lb") +
       brms::stanvar(sigma_ub, "sigma_ub")
-  }
-
-
-  # ----- dn -----
-
-  if (isFALSE(bp)) {
-    # ----- set prirors -----
-
-    priors_params <-
+    }
+    )
+  } else {
+    with(params_env, {
       brms::stanvar(a, name = "a") +
       brms::stanvar(b, "b") +
       brms::stanvar(dn, "dn") +
@@ -395,6 +205,8 @@ two_source_priors_params_arc <- function(
       brms::stanvar(tp_ub, "tp_ub") +
       brms::stanvar(sigma_lb, "sigma_lb") +
       brms::stanvar(sigma_ub, "sigma_ub")
+    }
+    )
   }
 
   return(priors_params)
diff --git a/R/utils.R b/R/utils.R
new file mode 100644
index 0000000..c42dcb5
--- /dev/null
+++ b/R/utils.R
@@ -0,0 +1,177 @@
+#' Error functions
+#' @param x prior to check
+#' @param arg_name the name of the argument to check.
+#'
+#' @name error_functions
+#' @keywords internal
+
+check_column_names <- function(x,
+                               arg_name = NULL) {
+
+  if (is.null(arg_name)) {
+    arg_name <- rlang::as_label(rlang::enexpr(x))
+  }
+
+  rv <- c("d13c", "c1", "c2")
+
+  if (!all(rv %in% names(x))) {
+    mv <- setdiff(rv, names(x))
+
+    cli::cli_abort(c(
+      "`{arg_name}` is missing: {mv}",
+      "i" = "Please provide {mv}"
+    ))
+  }
+}
+
+#' @param x prior to check
+#' @param arg_name the name of the argument to check.
+#' @name error_functions
+#' @keywords internal
+
+check_data_frame <- function(x,
+                             arg_name = NULL) {
+
+  if (is.null(arg_name)) {
+    arg_name <- rlang::as_label(rlang::enexpr(x))
+  }
+
+  if (!(inherits(x, c("data.frame", "tibble", "data.table")))) {
+    cli::cli_abort(c(
+      "`{arg_name}` must be a data.frame, tibble, or data.table",
+      "i" = "Please provide data.frame"
+    ))
+  }
+}
+
+
+#' @param x prior to check
+#' @param arg_name the name of the argument to check.
+#' @name error_functions
+#' @keywords internal
+check_lambda <- function(x,
+                         arg_name = NULL) {
+
+  if (is.null(arg_name)) {
+    arg_name <- rlang::as_label(rlang::enexpr(x))
+  }
+
+  if (!(is.numeric(x)) || !(x %in% c(1, 2))) {
+    cli::cli_abort(c(
+      "`{arg_name}` argument must be a numeric value and either `1` or `2`",
+      "i" = "Please provide `1` or `2`"
+    ))
+  }
+}
+
+
+#' @param x prior to check
+#' @param arg_name the name of the argument to check.
+#'
+#' @name error_functions
+#' @keywords internal
+
+check_logical <- function(x, arg_name = NULL) {
+
+  if (is.null(arg_name)) {
+    arg_name <- rlang::as_label(rlang::enexpr(x))
+  }
+
+  if (!(is.logical(x))) {
+    cli::cli_abort(c(
+      "`{arg_name}` argument must be a logical value",
+      "i" = "Please provide TRUE or FALSE"
+    ))
+  }
+}
+
+#' @param x prior to check
+#'  @param arg_name the name of the argument to check.
+#'
+#' @name error_functions
+check_numerical <- function(x, arg_name = NULL) {
+
+  if (is.null(arg_name)) {
+    arg_name <- rlang::as_label(rlang::enexpr(x))
+  }
+
+  if (!is.numeric(x) || length(x) != 1) {
+    cli::cli_abort(c(
+      "`{arg_name}` argument must be a numerical value.",
+      "i" = "Please provide a numerical value"
+    ))
+  }
+}
+
+#' Set default priors
+#' @param model model type
+#' @name set_priors
+#' @keywords internal
+
+default_priors <- function(model = c(
+  "one_source",
+  "two_source",
+  "two_source_ar",
+  "two_source_arc"
+)) {
+
+  model <- match.arg(model)
+
+  base_defaults <- list(
+    dn = 3.4,
+    dn_sigma = 0.25,
+    tp_lb = 2,
+    tp_ub = 10,
+    sigma_lb = 0,
+    sigma_ub = 10
+  )
+
+  model_specific <- list(
+
+    one_source = list(
+      n1 = 9,
+      n1_sigma = 1
+    ),
+
+    two_source = list(
+      a = 1,
+      b = 1,
+      c1 = -21,
+      c1_sigma = 1,
+      c2 = -26,
+      c2_sigma = 1,
+      n1 = 8,
+      n1_sigma = 1,
+      n2 = 9.5,
+      n2_sigma = 1
+    ),
+
+    two_source_ar = list(
+      a = 1,
+      b = 1,
+      n1 = 8,
+      n1_sigma = 1,
+      n2 = 9.5,
+      n2_sigma = 1
+    ),
+
+    two_source_arc = list(
+      a = 1,
+      b = 1,
+      n1 = 8,
+      n1_sigma = 1,
+      n2 = 9.5,
+      n2_sigma = 1,
+      c1 = -21,
+      c1_sigma = 1,
+      c2 = -26,
+      c2_sigma = 1
+    )
+  )
+
+  # Merge: specific overrides base
+  c(model_specific[[model]],
+    base_defaults)
+}
+
+
diff --git a/R/zzz.R b/R/zzz.R
index 7955010..2ce19ff 100644
--- a/R/zzz.R
+++ b/R/zzz.R
@@ -1,27 +1,29 @@
 .onAttach <- function(libname, pkgname) {
-  packageStartupMessage("version 0.1.0 ('one-skate').\nHave you loaded {brms}?")
+  packageStartupMessage("version 0.1.1 ('two-skate').\nHave you loaded {brms}?")
 }
 utils::globalVariables(c(
-  "n1",
-  "n1_sigma",
-  "normal",
-  "uniform",
+  "a",
   "alpha",
-  "min_alpha",
-  "max_alpha",
-  "d13c",
+  "b",
   "c1",
   "c2",
+  "c1_mean",
+  "c2_mean",
+  "c1_sigma",
+  "c2_sigma",
+  "d13c",
   "dn",
   "dn_sigma",
+  "max_alpha",
+  "min_alpha",
+  "n1",
+  "n2",
+  "n1_sigma",
+  "n2_sigma",
+  "normal",
   "sigma_lb",
-  "sigma_ub", "tp_lb",
+  "sigma_ub",
+  "tp_lb",
   "tp_ub",
-  "c1_mean",
-  "c2_mean", "n2",
-  "n2_sigma",
-  "c1_sigma",
-  "c2_sigma",
-  "a",
-  "b"
+  "uniform"
 ))
diff --git a/man/error_functions.Rd b/man/error_functions.Rd
new file mode 100644
index 0000000..5106d80
--- /dev/null
+++ b/man/error_functions.Rd
@@ -0,0 +1,31 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/utils.R
+\name{error_functions}
+\alias{error_functions}
+\alias{check_column_names}
+\alias{check_data_frame}
+\alias{check_lambda}
+\alias{check_logical}
+\alias{check_numerical}
+\title{Error functions}
+\usage{
+check_column_names(x, arg_name = NULL)
+
+check_data_frame(x, arg_name = NULL)
+
+check_lambda(x, arg_name = NULL)
+
+check_logical(x, arg_name = NULL)
+
+check_numerical(x, arg_name = NULL)
+}
+\arguments{
+\item{x}{prior to check
+@param arg_name the name of the argument to check.}
+
+\item{arg_name}{the name of the argument to check.}
+}
+\description{
+Error functions
+}
+\keyword{internal}
diff --git a/man/set_priors.Rd b/man/set_priors.Rd
new file mode 100644
index 0000000..2f3b865
--- /dev/null
+++ b/man/set_priors.Rd
@@ -0,0 +1,18 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/utils.R
+\name{set_priors}
+\alias{set_priors}
+\alias{default_priors}
+\title{Set default priors}
+\usage{
+default_priors(
+  model = c("one_source", "two_source", "two_source_ar", "two_source_arc")
+)
+}
+\arguments{
+\item{model}{model type}
+}
+\description{
+Set default priors
+}
+\keyword{internal}
diff --git a/man/trps-package.Rd b/man/trps-package.Rd
index 9dc2988..89bfa98 100644
--- a/man/trps-package.Rd
+++ b/man/trps-package.Rd
@@ -4,7 +4,7 @@
 \name{trps-package}
 \alias{trps}
 \alias{trps-package}
-\title{trps: Bayesian Trophic Position Models using 'stan'}
+\title{trps: Bayesian Trophic Position Models using 'Stan'}
 \description{
 \if{html}{\figure{logo.png}{options: style='float: right' alt='logo' width='120'}}
 
diff --git a/tests/testthat/test-add_alpha.R b/tests/testthat/test-add_alpha.R
index ad734ec..256f734 100644
--- a/tests/testthat/test-add_alpha.R
+++ b/tests/testthat/test-add_alpha.R
@@ -31,7 +31,7 @@ test_that("test check if alpha errors ", {
 test_that("test check if alpha errors ", {
   expect_error(
     add_alpha(data = combined_iso[-c(4, 10, 12)]),
-    "The data.frame is missing: d13c, c1, and c2"
+    "`data` is missing: d13c, c1, and c2"
   )
 })
 
diff --git a/tests/testthat/test-one_source_priors_params.R b/tests/testthat/test-one_source_priors_params.R
index 602834c..6065962 100644
--- a/tests/testthat/test-one_source_priors_params.R
+++ b/tests/testthat/test-one_source_priors_params.R
@@ -306,9 +306,9 @@ test_that("test one-source priors sigma_ub", {
 
 test_that("test priors fails sigma_ub ", {
   expect_error(
-    one_source_priors_params(,
+    one_source_priors_params(
       sigma_ub = "test"
     ),
-    regexp = "`sigma_ub` argument must be a numerical value"
+    regexp = "`sigma_ub` argument must be a numerical value."
   )
 })
diff --git a/vignettes/article/estimate_trophic_position_two_source_model_ar.Rmd b/vignettes/article/estimate_trophic_position_two_source_model_ar.Rmd
index 95308c9..24eee9a 100644
--- a/vignettes/article/estimate_trophic_position_two_source_model_ar.Rmd
+++ b/vignettes/article/estimate_trophic_position_two_source_model_ar.Rmd
@@ -56,7 +56,7 @@ from above, $\alpha_{min}$ is the minimum value of $\alpha$ calculated above, an
 
 $$
 \text{Trophic Position} = \lambda + \frac{(\delta^{15}N_c - 
-[(\delta^{15}N_{b1} \times \alpha_r) - (\delta^{15}N_{b1} \times (1 - \alpha_r))]}{\Delta N}
+[(\delta^{15}N_{b1} \times \alpha_r) + (\delta^{15}N_{b2} \times (1 - \alpha_r))]}{\Delta N}
 $$