Throughout the Treatise, Berkeley inveighs against the “doctrine of abstraction,” which he characterizes as a “fine and subtle net […] which has so miserably perplexed and entangled the minds of men” (21). By the “doctrine of abstraction,” Berkeley means the proposition, current in the philosophy of his day, that the human mind can form ideas of abstract concepts. The doctrine of abstraction maintains that we cannot only see a particular man but can also conceive of “man” as a general concept. Not only can we see the color red, but we can also conceive of “color” as a general concept without reference to a specific color, such as red, blue, or white.

This premise is false, Berkeley argues, because in thinking about the idea “color” we are always thinking about a particular color; we cannot actually think of an abstract or nonspecific “color.” An overreliance on abstraction in our thinking gradually brings us away from the simple truth of things as they are, introducing doubt and skepticism about our ability to discover truth. Thus, for Berkeley, abstraction eventually leads to an absurd questioning of everything, whereas the true goal of philosophy is to arrive at settled convictions.