diff --git a/NAMESPACE b/NAMESPACE
index c5ff88f..e4bf812 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -39,6 +39,9 @@ export(fixed_to_BP)
 export(fixed_to_CE)
 export(fixed_to_b2k)
 export(fixed_to_julian)
+export(is_calendar)
+export(is_gregorian)
+export(is_julian)
 export(year_axis)
 exportClasses(RataDie)
 exportClasses(TimeIntervals)
@@ -67,8 +70,6 @@ exportMethods(frequency)
 exportMethods(get_calendar)
 exportMethods(image)
 exportMethods(intervals)
-exportMethods(is_gregorian)
-exportMethods(is_julian)
 exportMethods(overlap)
 exportMethods(plot)
 exportMethods(pretty)
diff --git a/R/AllGenerics.R b/R/AllGenerics.R
index 52fcb97..14a6c70 100644
--- a/R/AllGenerics.R
+++ b/R/AllGenerics.R
@@ -174,33 +174,6 @@ setGeneric(
   valueClass = "TimeScale"
 )
 
-#' Is an Object a Calendar?
-#'
-#' Test inheritance relationships between an object and a calendar class.
-#' @param object Any \R object.
-#' @return
-#'  A [`logical`] vector.
-#' @author N. Frerebeau
-#' @docType methods
-#' @family calendar tools
-#' @name is
-#' @rdname is
-NULL
-
-#' @rdname is
-#' @aliases is_gregorian-method
-setGeneric(
-  name = "is_gregorian",
-  def = function(object) standardGeneric("is_gregorian")
-)
-
-#' @rdname is
-#' @aliases is_julian-method
-setGeneric(
-  name = "is_julian",
-  def = function(object) standardGeneric("is_julian")
-)
-
 #' Calendar Parameters
 #'
 #' @param object A [`TimeScale-class`] object.
diff --git a/R/calendar-gregorian.R b/R/calendar-gregorian.R
index 666c2c5..53ba4c8 100644
--- a/R/calendar-gregorian.R
+++ b/R/calendar-gregorian.R
@@ -2,18 +2,6 @@
 #' @include AllGenerics.R
 NULL
 
-# Gregorian calendar ===========================================================
-#' @export
-#' @rdname is
-#' @aliases is_gregorian,ANY-method
-setMethod(
-  f = "is_gregorian",
-  signature = "ANY",
-  definition = function(object) {
-    methods::is(object, "GregorianCalendar")
-  }
-)
-
 # Fixed from Gregorian =========================================================
 #' @export
 #' @rdname fixed
diff --git a/R/calendar-julian.R b/R/calendar-julian.R
index b6165ef..adc5ea4 100644
--- a/R/calendar-julian.R
+++ b/R/calendar-julian.R
@@ -2,18 +2,6 @@
 #' @include AllGenerics.R
 NULL
 
-# Julian calendar ==============================================================
-#' @export
-#' @rdname is
-#' @aliases is_julian,ANY-method
-setMethod(
-  f = "is_julian",
-  signature = "ANY",
-  definition = function(object) {
-    methods::is(object, "JulianCalendar")
-  }
-)
-
 # Fixed from Julian ============================================================
 #' @export
 #' @rdname fixed
diff --git a/R/calendar.R b/R/calendar.R
index fd020ba..5f14785 100644
--- a/R/calendar.R
+++ b/R/calendar.R
@@ -132,6 +132,33 @@ setMethod(
   }
 )
 
+# Predicates ===================================================================
+#' Is an Object a Calendar?
+#'
+#' Test inheritance relationships between an object and a calendar class.
+#' @param object Any \R object.
+#' @return
+#'  A [`logical`] scalar.
+#' @author N. Frerebeau
+#' @docType methods
+#' @family calendar tools
+#' @export
+is_calendar <- function(object) {
+  methods::is(object, "TimeScale")
+}
+
+#' @export
+#' @rdname is_calendar
+is_gregorian <- function(object) {
+  methods::is(object, "GregorianCalendar")
+}
+
+#' @export
+#' @rdname is_calendar
+is_julian <- function(object) {
+  methods::is(object, "JulianCalendar")
+}
+
 # Mutators =====================================================================
 ## Getters ---------------------------------------------------------------------
 #' @export
diff --git a/inst/tinytest/test_calendar.R b/inst/tinytest/test_calendar.R
index f0916ff..f7e5869 100644
--- a/inst/tinytest/test_calendar.R
+++ b/inst/tinytest/test_calendar.R
@@ -16,6 +16,7 @@ expect_error(calendar("XXX"), "Unknown calendar")
 # Gregorian calendar ===========================================================
 G <- calendar("BP")
 
+expect_true(is_calendar(G))
 expect_true(is_gregorian(G))
 expect_false(is_julian(G))
 
@@ -30,6 +31,7 @@ expect_identical(calendar_year(G), 365.2425)
 # Julian calendar ==============================================================
 J <- calendar("julian")
 
+expect_true(is_calendar(J))
 expect_true(is_julian(J))
 expect_false(is_gregorian(J))
 
diff --git a/man/calendar.Rd b/man/calendar.Rd
index 9dc13db..066ea2b 100644
--- a/man/calendar.Rd
+++ b/man/calendar.Rd
@@ -55,7 +55,7 @@ Other calendar tools:
 \code{\link{convert}()},
 \code{\link{get_calendar}()},
 \code{\link{gregorian}},
-\code{\link{is}()},
+\code{\link{is_calendar}()},
 \code{\link{julian}()}
 }
 \author{
diff --git a/man/calendar_get.Rd b/man/calendar_get.Rd
index 3a871fe..ff99a8d 100644
--- a/man/calendar_get.Rd
+++ b/man/calendar_get.Rd
@@ -100,7 +100,7 @@ Other calendar tools:
 \code{\link{convert}()},
 \code{\link{get_calendar}()},
 \code{\link{gregorian}},
-\code{\link{is}()},
+\code{\link{is_calendar}()},
 \code{\link{julian}()}
 }
 \author{
diff --git a/man/convert.Rd b/man/convert.Rd
index e47cf3a..63623d4 100644
--- a/man/convert.Rd
+++ b/man/convert.Rd
@@ -47,7 +47,7 @@ Other calendar tools:
 \code{\link{calendar_get}},
 \code{\link{get_calendar}()},
 \code{\link{gregorian}},
-\code{\link{is}()},
+\code{\link{is_calendar}()},
 \code{\link{julian}()}
 }
 \author{
diff --git a/man/get_calendar.Rd b/man/get_calendar.Rd
index a995f1d..21336d8 100644
--- a/man/get_calendar.Rd
+++ b/man/get_calendar.Rd
@@ -51,7 +51,7 @@ Other calendar tools:
 \code{\link{calendar_get}},
 \code{\link{convert}()},
 \code{\link{gregorian}},
-\code{\link{is}()},
+\code{\link{is_calendar}()},
 \code{\link{julian}()}
 }
 \author{
diff --git a/man/gregorian.Rd b/man/gregorian.Rd
index bfa65a0..6681af3 100644
--- a/man/gregorian.Rd
+++ b/man/gregorian.Rd
@@ -51,7 +51,7 @@ Other calendar tools:
 \code{\link{calendar_get}},
 \code{\link{convert}()},
 \code{\link{get_calendar}()},
-\code{\link{is}()},
+\code{\link{is_calendar}()},
 \code{\link{julian}()}
 }
 \author{
diff --git a/man/is.Rd b/man/is_calendar.Rd
similarity index 62%
rename from man/is.Rd
rename to man/is_calendar.Rd
index 124511a..cefe140 100644
--- a/man/is.Rd
+++ b/man/is_calendar.Rd
@@ -1,30 +1,23 @@
 % Generated by roxygen2: do not edit by hand
-% Please edit documentation in R/AllGenerics.R, R/calendar-gregorian.R,
-%   R/calendar-julian.R
+% Please edit documentation in R/calendar.R
 \docType{methods}
-\name{is}
-\alias{is}
+\name{is_calendar}
+\alias{is_calendar}
 \alias{is_gregorian}
-\alias{is_gregorian-method}
 \alias{is_julian}
-\alias{is_julian-method}
-\alias{is_gregorian,ANY-method}
-\alias{is_julian,ANY-method}
 \title{Is an Object a Calendar?}
 \usage{
+is_calendar(object)
+
 is_gregorian(object)
 
 is_julian(object)
-
-\S4method{is_gregorian}{ANY}(object)
-
-\S4method{is_julian}{ANY}(object)
 }
 \arguments{
 \item{object}{Any \R object.}
 }
 \value{
-A \code{\link{logical}} vector.
+A \code{\link{logical}} scalar.
 }
 \description{
 Test inheritance relationships between an object and a calendar class.
diff --git a/man/julian.Rd b/man/julian.Rd
index 7a17dff..3a09862 100644
--- a/man/julian.Rd
+++ b/man/julian.Rd
@@ -37,7 +37,7 @@ Other calendar tools:
 \code{\link{convert}()},
 \code{\link{get_calendar}()},
 \code{\link{gregorian}},
-\code{\link{is}()}
+\code{\link{is_calendar}()}
 }
 \author{
 N. Frerebeau