Berkeley understands two contemporary obstacles to attaining knowledge. The first is the principle that material things exist outside of the mind. The second is the emphasis on abstract ideas. In this group of sections, Berkeley discusses the second obstacle, the dangers of abstract thought.

The problem with abstract thought is that it makes ordinary things seem “strangely difficult and incomprehensible” (70). Time exemplifies this type of abstraction. Philosophers treat time as duration, separate from the “succession of ideas” (70) and actions that characterize time as we experience it..

Abstract thought assumes that we can form an idea like happiness or virtue as abstracted from individual instances of happiness or virtue. Berkeley denies that we can do this and argues that belief in such abstraction has hindered knowledge and “rendered morality difficult” (72).

Abstract thought is closely related to skepticism. Skepticism claims that our senses deceive us and therefore “the real essence” and “internal qualities” of things are “hidden from our view” (72). This way of thinking is “groundless” and influences us “to mistrust our senses and think we know nothing of those things which we perfectly comprehend” (72).

Berkeley sees as the source of these errors in the principle that “everything includes within itself the cause of its properties” (72).