diff --git a/NAMESPACE b/NAMESPACE
index c5ff88f..514c173 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -67,6 +67,7 @@ exportMethods(frequency)
 exportMethods(get_calendar)
 exportMethods(image)
 exportMethods(intervals)
+exportMethods(is_calendar)
 exportMethods(is_gregorian)
 exportMethods(is_julian)
 exportMethods(overlap)
diff --git a/R/AllGenerics.R b/R/AllGenerics.R
index 52fcb97..1229a90 100644
--- a/R/AllGenerics.R
+++ b/R/AllGenerics.R
@@ -179,22 +179,24 @@ setGeneric(
 #' Test inheritance relationships between an object and a calendar class.
 #' @param object Any \R object.
 #' @return
-#'  A [`logical`] vector.
+#'  A [`logical`] scalar.
 #' @author N. Frerebeau
 #' @docType methods
 #' @family calendar tools
-#' @name is
-#' @rdname is
-NULL
+#' @aliases is_calendar-method
+setGeneric(
+  name = "is_calendar",
+  def = function(object) standardGeneric("is_calendar")
+)
 
-#' @rdname is
+#' @rdname is_calendar
 #' @aliases is_gregorian-method
 setGeneric(
   name = "is_gregorian",
   def = function(object) standardGeneric("is_gregorian")
 )
 
-#' @rdname is
+#' @rdname is_calendar
 #' @aliases is_julian-method
 setGeneric(
   name = "is_julian",
diff --git a/R/calendar-gregorian.R b/R/calendar-gregorian.R
index 666c2c5..498edf1 100644
--- a/R/calendar-gregorian.R
+++ b/R/calendar-gregorian.R
@@ -4,7 +4,7 @@ NULL
 
 # Gregorian calendar ===========================================================
 #' @export
-#' @rdname is
+#' @rdname is_calendar
 #' @aliases is_gregorian,ANY-method
 setMethod(
   f = "is_gregorian",
diff --git a/R/calendar-julian.R b/R/calendar-julian.R
index b6165ef..a790adb 100644
--- a/R/calendar-julian.R
+++ b/R/calendar-julian.R
@@ -4,7 +4,7 @@ NULL
 
 # Julian calendar ==============================================================
 #' @export
-#' @rdname is
+#' @rdname is_calendar
 #' @aliases is_julian,ANY-method
 setMethod(
   f = "is_julian",
diff --git a/R/calendar.R b/R/calendar.R
index fd020ba..44929a6 100644
--- a/R/calendar.R
+++ b/R/calendar.R
@@ -132,6 +132,18 @@ setMethod(
   }
 )
 
+# Predicates ===================================================================
+#' @export
+#' @rdname is_calendar
+#' @aliases is_calendar,ANY-method
+setMethod(
+  f = "is_calendar",
+  signature = "ANY",
+  definition = function(object) {
+    methods::is(object, "TimeScale")
+  }
+)
+
 # 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 78%
rename from man/is.Rd
rename to man/is_calendar.Rd
index 124511a..79c2a1d 100644
--- a/man/is.Rd
+++ b/man/is_calendar.Rd
@@ -1,17 +1,21 @@
 % Generated by roxygen2: do not edit by hand
 % Please edit documentation in R/AllGenerics.R, R/calendar-gregorian.R,
-%   R/calendar-julian.R
+%   R/calendar-julian.R, R/calendar.R
 \docType{methods}
-\name{is}
-\alias{is}
+\name{is_calendar}
+\alias{is_calendar}
+\alias{is_calendar-method}
 \alias{is_gregorian}
 \alias{is_gregorian-method}
 \alias{is_julian}
 \alias{is_julian-method}
 \alias{is_gregorian,ANY-method}
 \alias{is_julian,ANY-method}
+\alias{is_calendar,ANY-method}
 \title{Is an Object a Calendar?}
 \usage{
+is_calendar(object)
+
 is_gregorian(object)
 
 is_julian(object)
@@ -19,12 +23,14 @@ is_julian(object)
 \S4method{is_gregorian}{ANY}(object)
 
 \S4method{is_julian}{ANY}(object)
+
+\S4method{is_calendar}{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