ISDATE() Date time function in SQL Server

What is ISDATE(Expression) ?

Returns 1 if the expression is a valid date, time, or datetime value; otherwise, 0.

Expression can be any character string , less than 4000 characters but it should not be Date datatype

Msg 8116, Level 16, State 1, Line 3
Argument data type date is invalid for argument 1 of isdate function.