The realist method starts with the whole in order to distinguish the parts. - Étienne Gilson

As used today, the word realism means in the first place the opposite to idealism when it claims that it is possible to pass from the subject to the object.

With Descartes the Cogito ergo sum [I think, therefore I am] turns into Cogito ergo res sunt [I think, therefore things are].

Every given reality implies the thought which apprehends it. Therefore being is the condition of knowing; knowing is not the condition of being.