BooleanQ

BooleanQ[expr] returns True if expr is True or False, False otherwise.

Attributes[BooleanQ] := {Protected}

Simple examples

In[1]:= BooleanQ[True]
Out[1]= True

In[2]:= BooleanQ[False]
Out[2]= True

In[3]:= BooleanQ[1]
Out[3]= False