Testing whether a mode is enabled

[Heime]

Am using icomplete-mode but find things somewhat confusing.

To enable or disable the mode one uses (icomplete-mode 1) and (icomplete-mode 
-1)

I want to test whether the mode is enabled or disabled with "(if 
icomplete-mode" and
(if (not icomplete-mode)".

(not OBJECT) returns t if OBJECT is nil, and returns nil otherwise.

When I use conditional with "icomplete-mode" is it correct to say that if 
"icomplete-mode" is nil,
then the mode is disabled?

I am uncertain because of the numeric values used to enable and disable.