A categorical proposition is a proposition that specifies some relationship between two categories or classes of things. All politicians are liars. Rubies are red. No philosopher is an idiot.
Some people are atheists.
Some lawyers are not crooks. Light rays travel at a fixed speed. Not all convicted murderers get the death penalty. Some students don't work very hard. A categorical proposition is in standard form only if it is expressed in one of the following four forms denoted by bold lettering.