Notes on <A Treatise Concerning the Principles of Human Knowledge> by George Berkeley
Introduction
Berkeley starts the book inquiring about the cause of Doubts and Difficulties, and proposes that it starts with the wrong use of our Faculties. He wants to discover the principles which introduced all the Doubtfulness and Uncertainty, to inquiry first principles of human knowledge. He examines the opinion that Mind has a power of framing Abstract Ideas or Notions of Things. Mind has the ability to separate out single abstract idea from all ideas mixed in the same Object. However, my imagination will not conceive the abstract idea without particulars. Here Berkeley refutes Locke’s opinion that the ability of getting abstract general ideas is tied to Language, and all Words must correspond to certain ideas, so the Words about general ideas corresponds to abstract general ideas, this is the classical conceptualist position. Berkeley’s position is a nominalist one, which says we don’t have a corresponding abstract general ideas for the general Words, whenever we think of general ideas, like Motion or Extension, we think of some particular motion with particular extension. The proposition involving general ideas just means it does not matter what particular Extension we think about, the proposition always hold true. Berkeley provides further arguments for the nominalist position by observing how Ideas become general. He is not denying there are general Ideas, but only that there are abstract general Ideas. An idea becomes general by representing all different ideas of the same sort. And for example Line becomes General, by being made a Sign of an abstract or general Line, and the name Line is also made General by being a Sign. And as the idea of general Line owes its generality to its being the Sign of an abstract or general Line, so the name Line must be thought to derive its Generality from the same Cause, namely the various particular Lines which it denotes.
Of the Principles of Human Knowledge
The Objects of Human Knowledge are either Ideas imprinted in the Senses, or perceived by attending to the Passions and Operations of the Mind, or Ideas from Memory and Imagination, Ideas that compounding, dividing or representing the ones of previous categories.
Besides the Objects of Knowledge, there is also the subject of knowledge, which is known as Mind, Spirit, Soul or my Self, which denotes the thing that is distinct from the Ideas. And the Existence of an Idea consists in being perceived.
That neither Thoughts, Passions, nor Ideas from Imagination exist without the Mind is evident, and it seems that Ideas imprinted on the Sense cannot exist otherwise than in a Mind perceiving them. Esse is Percipi, the Existence of unthinking things don’t have any Existence out of the Minds or thinking Things which perceive them.
Berkeley compares the common conception that people have about things can exist independent of Minds to the confusion of the Abstract General Ideas. People can easily distinguish the Existence of sensible Objects from their being perceived by conceiving them Existing unperceived. But Things we can see and feel are only Sensations, we cannot separate them, even in thought, from Perception. As it is impossible for me to see or feel any Thing without an actual Sensation of that Thing, so is it impossible for me to conceive in my Thoughts any sensible Thing or Object distinct from the Sensation or Perception of it.
From what has been said, it follows, there is not any other Substance than Spirit, or that which perceives.
Also, primary qualities like Extension, Figure and Motion are only Ideas that exist in the Mind just like secondary qualities like Color. This can be demonstrated by the fact that we cannot conceive the Extension and Motion of a Body without all other sensible Qualities.
Berkeley also comments that even there is Material Substances exist without the Mind, we can not know this. Because we can only know either by Sense or by Reason. From Sense we only have knowledge of our Senses, and they do not inform us things exist without the Mind, or unperceived. So if we have any Knowledge at all of external Things, it must be by Reason, by inferring the existence of the Bodies from what is perceived by Sense. But since we can’t pretend that there is any necessary connection between the external Bodies and our Ideas, so it is possible we might be affect with all the Ideas we have now, and no Bodies existed resembling these Ideas(This is very similar to the proposition that there is no abstract general ideas corresponding to the words representing general ideas).
People might argue that assuming the existence of External Bodies helps to explain the manner of their Production, but that is not the case since even there are External Bodies, it’s still not clear how it imprint any Idea in the Mind. It is equally inexplicable with or without this Supposition.
In short, if there were external Bodies, it is impossible we should ever come to know it; and if there were not, we might have the very same Reasons to think there were that we have now.
You may ask then what is the cause of our ideas of Being? Berkeley’s answer is that because no material Substance can cause Ideas, the Cause of Ideas must be incorporeal active Substance or Spirit. The Ideas imprinted on the Senses by the Author of Nature are called real Things.
There might be some misunderstanding that Berkeley is arguing that the things that we can apprehend in daily life does not exist, but that is not the case. Berkeley says the only thing whose Existence we deny is that which Philosophers call Matter or corporeal Substance.
Also Berkeley explains that his Ideas can refer to what is called Thing by custom. Reason he did it is because the Term Thing is generally supposed to denote somewhat existing without the Mind, secondly because Thing has a more comprehensive Signification than Idea, including Spirits and Ideas.
There are more responses to objections in the book, but I’ll stop here because I feel the main idea is clear. I think what Berkeley is trying to say is more about the interpretation, or meaning of “existence”. He thinks that there is no concept of existence without Mind or Perception, which makes sense. But the ordinary meaning of the existence of unthinking Substance is that there are things outside of Mind, that’s not really influenced by Mind which causes the perception of Mind(which has its own problem that how does a Substance causes Idea). To which Berkeley might say that this concept of unthinking Substance is only out of convenience, we can’t claim that it exist, just like the concept of abstract general ideas, and Berkeley believes the Ideas are can be caused only by Spirit.