diff --git a/R/Rules-methods.R b/R/Rules-methods.R
index fe660b8c3..919329bb3 100644
--- a/R/Rules-methods.R
+++ b/R/Rules-methods.R
@@ -3017,7 +3017,7 @@ setMethod("stopTrial",
       prob_target <- stopping@prob_target
 
       ## checks
-      stopifnot(is.probability(prob_target))
+      assert_probability(prob_target)
       stopifnot(is(Effmodel, "ModelEff"))
       stopifnot(is(Effsamples, "Samples"))
       stopifnot(is.function(TDderive))
@@ -3135,7 +3135,7 @@ setMethod("stopTrial",
       prob_target <- stopping@prob_target
 
       ## checks
-      stopifnot(is.probability(prob_target))
+      assert_probability(prob_target)
       stopifnot(is(Effmodel, "ModelEff"))
 
 
diff --git a/R/fromQuantiles.R b/R/fromQuantiles.R
index 860b8201e..4513b736e 100644
--- a/R/fromQuantiles.R
+++ b/R/fromQuantiles.R
@@ -76,8 +76,10 @@ Quantiles2LogisticNormal <- function(dosegrid,
                                        )) {
   ## extracts and checks
   nDoses <- length(dosegrid)
+
   assert_flag(logNormal)
   assert_flag(verbose)
+  assert_probability(level, bounds_closed = FALSE)
   stopifnot(
     !is.unsorted(dosegrid, strictly = TRUE),
     ## the medians must be monotonically increasing:
@@ -87,7 +89,6 @@ Quantiles2LogisticNormal <- function(dosegrid,
     identical(length(upper), nDoses),
     all(lower < median),
     all(upper > median),
-    is.probability(level, bounds = FALSE),
     identical(length(parlower), 5L),
     identical(length(parupper), 5L),
     all(parlower < parstart),
@@ -234,10 +235,8 @@ Quantiles2LogisticNormal <- function(dosegrid,
 ##' @export
 ##' @keywords programming
 getMinInfBeta <- function(p, q) {
-  stopifnot(
-    is.probability(p, bounds = FALSE),
-    is.probability(q, bounds = FALSE)
-  )
+  assert_probability(p, bounds_closed = FALSE)
+  assert_probability(q, bounds_closed = FALSE)
 
   ret <-
     if (q > p) {
@@ -309,12 +308,13 @@ MinimalInformative <- function(dosegrid,
                                ...) {
   ## extracts and checks
   nDoses <- length(dosegrid)
+
+  assert_probability(threshmin, bounds_closed = FALSE)
+  assert_probability(threshmax, bounds_closed = FALSE)
+  assert_probability(probmin, bounds_closed = FALSE)
+  assert_probability(probmax, bounds_closed = FALSE)
   stopifnot(
-    !is.unsorted(dosegrid, strictly = TRUE),
-    is.probability(threshmin, bounds = FALSE),
-    is.probability(threshmax, bounds = FALSE),
-    is.probability(probmin, bounds = FALSE),
-    is.probability(probmax, bounds = FALSE)
+    !is.unsorted(dosegrid, strictly = TRUE)
   )
   xmin <- dosegrid[1]
   xmax <- dosegrid[nDoses]
diff --git a/R/helpers.R b/R/helpers.R
index 2c3e077be..75b933b95 100644
--- a/R/helpers.R
+++ b/R/helpers.R
@@ -127,47 +127,6 @@ safeInteger <- function(x) {
   as.integer(x)
 }
 
-##' Predicate checking for a probability
-##'
-##' @param x the object being checked
-##' @param bounds whether to include the bounds 0 and 1 (default)
-##' @return Returns \code{TRUE} if \code{x} is a probability
-##'
-##' @keywords internal
-is.probability <- function(x,
-                           bounds = TRUE) {
-  if (bounds) {
-    return(test_numeric(x, lower = 0, upper = 1, any.missing = FALSE))
-  } else {
-    return(test_numeric(x, lower = 0, upper = 1, any.missing = FALSE) && x != 0 && x != 1)
-  }
-}
-
-##' Predicate checking for a numeric range
-##'
-##' @param x the object being checked
-##' @return Returns \code{TRUE} if \code{x} is a numeric range
-##'
-##' @keywords internal
-is.range <- function(x) {
-  return(identical(length(x), 2L) &&
-    x[1] < x[2])
-}
-
-##' Predicate checking for a probability range
-##'
-##' @param x the object being checked
-##' @param bounds whether to include the bounds 0 and 1 (default)
-##' @return Returns \code{TRUE} if \code{x} is a probability range
-##'
-##' @keywords internal
-is.probRange <- function(x,
-                         bounds = TRUE) {
-  return(is.range(x) &&
-    all(sapply(x, is.probability, bounds = bounds)))
-}
-
-
 ##' Shorthand for logit function
 ##'
 ##' @param x the function argument
diff --git a/man/is.probRange.Rd b/man/is.probRange.Rd
deleted file mode 100644
index e27fd5f60..000000000
--- a/man/is.probRange.Rd
+++ /dev/null
@@ -1,20 +0,0 @@
-% Generated by roxygen2: do not edit by hand
-% Please edit documentation in R/helpers.R
-\name{is.probRange}
-\alias{is.probRange}
-\title{Predicate checking for a probability range}
-\usage{
-is.probRange(x, bounds = TRUE)
-}
-\arguments{
-\item{x}{the object being checked}
-
-\item{bounds}{whether to include the bounds 0 and 1 (default)}
-}
-\value{
-Returns \code{TRUE} if \code{x} is a probability range
-}
-\description{
-Predicate checking for a probability range
-}
-\keyword{internal}
diff --git a/man/is.probability.Rd b/man/is.probability.Rd
deleted file mode 100644
index c83356096..000000000
--- a/man/is.probability.Rd
+++ /dev/null
@@ -1,20 +0,0 @@
-% Generated by roxygen2: do not edit by hand
-% Please edit documentation in R/helpers.R
-\name{is.probability}
-\alias{is.probability}
-\title{Predicate checking for a probability}
-\usage{
-is.probability(x, bounds = TRUE)
-}
-\arguments{
-\item{x}{the object being checked}
-
-\item{bounds}{whether to include the bounds 0 and 1 (default)}
-}
-\value{
-Returns \code{TRUE} if \code{x} is a probability
-}
-\description{
-Predicate checking for a probability
-}
-\keyword{internal}
diff --git a/man/is.range.Rd b/man/is.range.Rd
deleted file mode 100644
index fbcea09d6..000000000
--- a/man/is.range.Rd
+++ /dev/null
@@ -1,18 +0,0 @@
-% Generated by roxygen2: do not edit by hand
-% Please edit documentation in R/helpers.R
-\name{is.range}
-\alias{is.range}
-\title{Predicate checking for a numeric range}
-\usage{
-is.range(x)
-}
-\arguments{
-\item{x}{the object being checked}
-}
-\value{
-Returns \code{TRUE} if \code{x} is a numeric range
-}
-\description{
-Predicate checking for a numeric range
-}
-\keyword{internal}