diff --git a/R/internals.R b/R/internals.R
new file mode 100644
index 0000000..3268434
--- /dev/null
+++ b/R/internals.R
@@ -0,0 +1,87 @@
+
+
+#' @title Abord bad argument
+#'
+#' @param arg An argument
+#' @param must What arg must be
+#' @param not Optional. What arg must not be.
+#'
+#' @return A stop statement
+abort_bad_argument <- function(arg, must, not = NULL) {
+  msg <- glue::glue("`{arg}` must {must}")
+  if (!is.null(not)) {
+    not <- typeof(not)
+    msg <- glue::glue("{msg}; not {not}.")
+  }
+
+  rlang::abort("error_bad_argument",
+               message = msg,
+               arg = arg,
+               must = must,
+               not = not
+  )
+}
+
+
+
+#' @title Stop statement "If not in colnames" with colnames
+#'
+#' @param .tbl A tibble
+#' @param cols A vector of column names (quoted)
+#' @param df Provide the tibble name as a character string
+#' @param arg Default to NULL.
+#'
+#' @return A stop statement
+if_not_in_stop <- function(.tbl, cols, df, arg = NULL){
+  if (is.null(arg)) {
+    msg <- glue::glue("The following column/s is/are missing in `{df}`:")
+  }
+  else {
+    msg <- glue::glue("The following column/s from `{arg}` is/are missing in `{df}`:")
+  }
+  if (!all(cols %in% colnames(.tbl))) {
+    rlang::abort(
+      c("Missing columns",
+        "*" =
+          paste(
+            msg,
+            paste(
+              subvec_not_in(cols, colnames(.tbl)),
+              collapse = ", ")
+          )
+      )
+    )
+  }
+}
+
+
+
+#' @title Stop statement "If not in vector"
+#'
+#' @param vec A vector of character strings
+#' @param cols A set of character strings
+#' @param vec_name Provide the vector name as a character string
+#' @param arg Default to NULL.
+#'
+#' @return A stop statement if some elements of vec are not in cols
+if_vec_not_in_stop <- function(vec, cols, vec_name, arg = NULL){
+  if (is.null(arg)) {
+    msg <- glue::glue("The following element/s is/are missing in `{vec_name}`:")
+  }
+  else {
+    msg <- glue::glue("The following element/s from `{arg}` is/are missing in `{vec_name}`:")
+  }
+  if (!all(cols %in% vec)) {
+    rlang::abort(
+      c("Missing elements",
+        "*" =
+          paste(
+            msg,
+            paste(
+              subvec_not_in(cols, vec),
+              collapse = ", ")
+          )
+      )
+    )
+  }
+}