What are the Microsoft Excel IS
Functions?
The IS functions are a set of computer
programs that you run from a worksheet cell formula. Their job
is to return a TRUE or FALSE value based upon a condition they
evaluate. These functions are basically your worksheet cell
value and worksheet formula error testers in logic. Here is a
list of the IS functions and what they do:
Function Name 
Definition 
ISBLANK Function 
Returns TRUE if its argument evaluates to blank, for
example an empty cell reference 
ISERR Function 
Detects an error in a formula used as its argument
and returns TRUE if detected, it ignores the #N/A
error value 
ISERROR Function 
Detects an error in a formula used as its argument
and returns TRUE if detected, covers all errors
(#N/A, #VALUE!, #REF!, #DIV/0!, #NUM!, #NAME?, or
#NULL!) 
ISLOGICAL Function 
Detects if its argument has the value of TRUE or
FALSE and returns TRUE if so 
ISNA Function 
Detects an #N/A error in a formula used as its
argument and returns TRUE if detected. It only
detects #N/A 
ISNONTEXT Function 
Detects if its argument is not a text value and
returns TRUE if so (Note that this function returns
TRUE if its argument refers to a blank cell) 
ISNUMBER Function 
Detects if its argument is a number and returns TRUE
if so 
ISREF Function 
Detects if its argument produces a value that can be
evaluated as a cell or range reference and returns
TRUE if so

ISTEXT Function 
Detects if its argument produces a text value and
returns TRUE if so

The IS functions can be used alone in a
worksheet formula as a flagging device when processing data on a
worksheet. For example, say you have rows of data on a worksheet
and you wanted to know if any of those rows had a number in a
particular column. You could use the ISNUMBER function to
evaluate that case and return TRUE/FALSE. You could then use
Excel's AutoFilter to filter on the TRUE/FALSE values returned.
The IS worksheet functions are also extremely useful when
developing error traps on your worksheet thus preventing your
worksheet formulas from generating errors a user can see. They
are also useful when designing dashboards especially
interpreting what a user has typed in a cell so a formula can
adjust to the input. They are very commonly used as a nested
function to the first argument of the IF function especially in
the cases of error protection and user value interpretation
(what the user types in a cell). The AND and OR functions also
heavily use these functions as nested functions in their
argument list. A complement to these functions is also the Excel
Data Validation feature which also helps protect against the
user typing the wrong values on a worksheet. Remember, locking
down what the user can type is always more effective then trying
to have a formula figure out what they typed. You run the IS
worksheet functions by typing their names in a formula then
followed by the information they are suppose to analyze.
How Do You Type the IS Worksheet
Functions in a Formula?
Whenever you type a formula in a
worksheet cell, this is called syntax or grammar. The general
syntax of the IS functions are like this when you type them in a
worksheet cell:
Function Name 
Argument Purpose 
= ISBLANK( value ) 
The value argument can be a cell reference, range
reference or formula that identifies a reference. If the
cell or range is blank, this function returns TRUE 
= ISERR( value ) 
The value argument can be a cell reference, range
reference or formula. If a calculation error is
produced excluding #N/A, this function returns TRUE 
= ISERROR( value ) 
The value argument can be a cell reference, range
reference or formula. If a calculation error is
produced including #N/A, this function returns TRUE 
= ISLOGICAL( value ) 
The value argument can be a constant, cell
reference, range reference or formula. If they
evaluate to TRUE or FALSE, this function returns
TRUE 
= ISNA( value ) 
The value argument can be a cell reference, range
reference or formula. If a calculation error is
produced generating #N/A, this function returns TRUE 
= ISNONTEXT( value ) 
The value argument can be a constant, cell
reference, range reference or formula. If argument
evaluates to a nontext value, this function returns
TRUE (Note that this function returns TRUE if the
value refers to a blank cell) 
= ISNUMBER( value ) 
The value argument can be a constant, cell
reference, range reference or formula. If argument
evaluates to a number value, this function returns
TRUE (Note that this function returns FALSE if the
value refers to a blank cell) 
= ISREF( value ) 
The value argument can be a formula. If argument
evaluates to an Excel range or cell reference, this
function returns TRUE (check out the INDIRECT
function)

= ISTEXT( value ) 
The value argument can be a constant, cell
reference, range reference or formula. If argument
evaluates to a text value, this function returns
TRUE (Note that this function returns FALSE if the
value refers to a blank cell)

Where value is called the function
argument list. Remember, you are running a computer program at
this point so the program needs information to operate and that
is why there is an argument list. When you see an argument list
and you see square brackets [ ] around the argument name, this
means the argument is optional and you do not have to include it
when typing unless you need it. So for the syntax above, all IS
functions take one argument when typing them in a worksheet cell
formula. What argument values can be used are discussed above
and below this paragraph. Remember functions expect certain
things in their argument lists, if you do not put the correct
information in the list they will generate an error when run.
How Do You Run the IS Functions?
Since the IS functions are computer
programs, they run when you press Enter to enter the formula
that contains them. If any of the arguments are wrong, the
function will return an error.
What Do I Type for an IS
Function Argument?
When typing the IS function in a
worksheet cell formula, you need to replace the value argument.
Some typical arguments you can use are:
Argument Type

Cell Formula

Example Explanation

Cell Reference

=ISNUMBER( A1 )

Determines if the value in cell A1 is a number 
Range Reference 
=ISTEXT( A1:A10 )

Determines if the values in cell A1:A10 are text 
Nested Function 
=IF( ISERROR( A1/A2 ), 0, A1/A2 )

ISERROR used as a nested function to the
IF function.
Determines if the formula A1/A2 (division by 0 is
always a problem) generates an error and if it does,
IF outputs 0 controlling the error. If no error then
IF outputs the calculated value of A1/A2 
Formula 
=ISREF( INDIRECT( "C1:C" & COUNTA( C:C )) )

Uses INDIRECT as
a nested function to build a range reference,
determines if INDIRECT generates a reference by
returning TRUE 
Cell and Range Names 
=ISBLANK( Sales_2012 )

Determines if the cell named Sales_2012 is blank * 
* It is possible to name a cell or
group of cells on a worksheet and use that name in place of
a range reference or cell reference. Consult Excel help on
how to name a cell.
Additional IS Function
Examples
The worksheet seen below contains
some typical worksheet formulas that run the IS worksheet
function. Pay close attention to the argument list and the
syntax used to write the formula.
Things to Know About the IS
Functions
 The value arguments of
the IS functions are not converted. Any numeric values
that are enclosed in double quotation marks are treated
as text. For example, in most other functions where a
number is required, the text value "19" is converted to
the number 19. However, in the formula ISNUMBER("19"),
"19" is not converted from a text value to a number
value, and the ISNUMBER function returns FALSE.
 The IS functions are
useful in formulas for testing the outcome of a
calculation. When combined with the IF function, these
functions provide a method for locating errors in
formulas.
