A Treatise Concerning the Principles of Human Knowledge

“My purpose therefore is to try if I can discover what those principles are which have introduced all that doubtfulness and uncertainty, those absurdities and contradictions, into the several sects of philosophy […]”

Berkeley plans to uncover the roots of skepticism, or a tendency in philosophy to inculcate doubt about our ability to attain knowledge. Berkeley argues that skepticism is fundamentally built on absurdity and contradiction, and thus can be exposed in a methodical way as a flawed way of thinking.

“Of late many have been very sensible of the absurd opinions and insignificant disputes which grow out of the abuse of words.”

Berkeley believes that skepticism is rooted in deceptions caused by the misuse of language. People are misled by using words in a vague or imprecise way or without understanding their meaning. “Insignificant disputes” implies that verbal misunderstanding causes needless arguments about minor philosophical points. Exposing the misuse of words and language is one of the major themes of the book.

“[T]he existence of an idea consists in being perceived.”

This passage is one of Berkeley’s main claims in the Treatise, which identifies existence with perception. The existence of “unthinking things” (i.e., non-spirits) depends upon their being perceived by some spirit. They do not have existence in their own right; rather, they exist for the sake of being perceived, whether that be by a human being, an animal, or God.

“Their esse is percipi, nor is it possible they should have any existence out of the minds or thinking things which perceive them.”

This passage is the formulation of Berkeley’s concept of existence. Berkeley uses Latin terms, reminiscent of medieval Scholastic philosophy, to express his conviction that sensible objects exist for the sake of, and only in, the perceptions of individual minds.

“For what are the forementioned objects but the things we perceive by sense? And what do we perceive besides our own ideas or sensations?”

Berkeley denies that “sensible objects” have an existence outside of the perceiving mind, which was a novel idea in his time. The quote reflects an understanding among empiricist philosophers that when we perceive something, we are perceiving not the object directly, but our ideas and sensations about the object.

“Some truths there are so near and obvious to the mind that a man need only open his eyes to see them.”

A consistent claim in the Treatise is that the truths Berkeley is proposing accord with common sense and our normal intuitions about reality. Here, Berkeley is referring to his doctrine that all sense objects exist only to be perceived, and that when not perceived, they either do not exist or exist in the mind of another spirit or of God. He considers it an “absurdity of abstraction” to believe that objects have “an existence independent of a spirit” (26).

“[T]here is not any other substance than Spirit, or that which perceives.”

Berkeley asserts his idealist view that spirit, not matter, is the fundamental basis of reality. The concept “Spirit” encompasses all intelligent life, including human beings and God. Berkeley argues that spirit exists, and matter does not; or, more precisely, matter exists only as something perceived in the mind of a spirit. Berkeley defines the principal activity of spirits as perception—a term which applies both to the operation of the senses and of the mind or intellect.

“I am not for disputing about the propriety, but the truth of the expression.”

Here, Berkeley is defending his use of the word “idea” to refer to sensible objects, or what most people would refer to as “things.” He insists on his usage of the word, even though it is novel. Berkeley uses the word because it precisely describes the shade of meaning he wants to convey, and this for him is more important than whether the usage will be socially acceptable.

“[T]hink with the learned and speak with the vulgar.”

Berkeley cites this adage in connection with his claim that spirit, rather than “natural causes,” is the source of perception. He claims that this is a nuanced, philosophical understanding of the nature of experience. Ordinary people believe that natural (i.e., secondary, intermediate) causes are real and operative, and thus we should use the language of natural causes in our discussions. This is characteristic of Berkeley’s philosophical outlook, enshrining a respect for common sense and a distrust for abstraction.

“[W]e are apt to lay too great a stress on analogies, and, to the prejudice of truth, humor that eagerness of the mind whereby it is carried to extend its knowledge into general theorems.”

This quote forms part of Berkey’s campaign against abstract thought. Characteristic of abstract thought is the tendency to form theorems that generalize from specific instances, thus enabling us to “extend our prospect beyond what is present and near to us” (74). However, such generalizing often turns out to be unwarranted and erroneous, relying on false analogies between things that are actually unalike.

“[I]t were highly to be wished that men of great abilities and obstinate application would draw off their thoughts from those amusements, and employ them in the study of such things as lie nearer the concerns of life, or have a more direct influence on the manners.”

Berkeley states his view that “speculative mathematics” is a field that has little use or application to life or the real world, and therefore mathematicians should give less attention to it. This is also part of Berkeley’s critique of abstraction in philosophy. He prefers fields of thought that address ethics and religious belief.

“What I am myself, that which I denote by the term I, is the same with what is meant by soul or spiritual substance.”

This quote is part of a passage in which Berkeley sharpens his distinction between spirit and ideas, the two classes of beings as he sees them. The common characteristic of ideas is that they are passive, whereas spirits are active—they perceive things and operate the faculties of reason and will. For this reason, he terms spirits substances, or things that exist in their own right, not dependent on or inhering in anything else.

“Nothing can be plainer than that the motions, changes, decays, and dissolutions which we hourly see befall natural bodies […] cannot possibly affect an active, simple, uncompounded substance […] that it to say, the soul of man is naturally immortal.”

As stated at the outset of the book, demonstrating the immortality of the soul is one of Berkeley’s goals, which he finally addresses in this passage. Berkeley uses an argument from Plato and Greek philosophy, the essence of which is that the soul is immortal because, being immaterial, it is not subject to decay or change.

“[T]he doctrine of abstract ideas has had no small share in rendering those sciences intricate and obscure which are particularly conversant about spiritual things.”

According to Berkeley, abstract thought is causing philosophy to become needlessly complicated and difficult to understand. Instead of defining clearly for people how they should live their lives, philosophy is lost in subtle, hair-splitting academic disputes. Berkeley considers that a reform is necessary, which he hopes to achieve through his book.

“It seems to be a general pretense of the unthinking herd that they cannot see God.”

Berkeley argues that unmistakable evidence of God’s existence is all around us in nature; the failure to deduce the fact of God’s existence is due to intellectual laziness. We know God from the effects He produces, just as we can see the effects brought about by human beings.

“[…] blinded with an excess of light […]”

Berkeley uses this phrase to describe the condition of those who do not believe that God exists. So great is the abundance of clear evidence all around them that, ironically, they are blinded to the reality of God’s presence. This memorable phrase anticipates Berkeley’s explicitly theological purpose, which he presents in the final portion of the book.

“[T]he operating according to general and stated laws is so necessary for our guidance in the affairs of life, and letting us into the secret of nature, that without it all reach and compass of thought, all human sagacity and design, could serve to no manner of purpose.”

Berkeley is considering whether the existence of natural causes proves that God does not cause things directly. He argues that God is in control but uses fixed laws to achieve his purposes. These laws allow us to discover the workings of nature through our reason, and those who are “unbiased and attentive” (101) will discern the hand of God behind them.

“We should further consider that the very blemishes and defects of nature are not without their use, in that they make an agreeable sort of variety and augment the beauty of the rest of creation, as shades in a picture serve to set off the brighter and more enlightened parts.”

Berkeley deals with the question of why evil or imperfect things exist and how their existence can be reconciled with God’s goodness. His basic argument is that evil exists to throw good into relief and that things that seem to be evil serve a purpose in the higher scheme of God’s plan. Here, Berkeley is writing in a long tradition of theodicy, or theological speculation on the problem of evil.

“Hence, it is plain that the splendid profusion of natural things should not be interpreted weakness or prodigality in the agent who produces them, but rather be looked on as an argument of the riches of his power.”

Extending the argument of the previous quote, Berkeley addresses the related question of why there is apparent wastefulness in nature. He answers that, since God is omnipotent and can produce anything at will, this should not be seen as waste but a manifestation of creative abundance.

“As for the mixture of pain or uneasiness which is in the world, pursuant to the general laws of nature, and the actions of finite, imperfect spirits, this, in the state we are in at present, is indispensably necessary to our well-being.”

This is the second part of Berkeley’s theodicy, or explanation of the existence of evil (see Quote 19). Berkeley contrasts the larger order and scheme of nature with the finite, limited, and imperfect nature of human beings. Given this discrepancy, there will be some things in nature that will not make immediate sense to us. However, all things are for our benefit, even if we do not understand it at the time.

“But what truth is there which shines so strongly on the mind that by an aversion of thought, a willful shutting of the eyes, we may not escape seeing it?”

Berkeley repeats the motif that the failure to sense God’s existence and goodness is due to a willful ignorance. Berkeley goes on to say that such ignorance is due to the fact that most people are occupied with “business and pleasure” (103) instead of philosophical reflection on the world around them.

“And yet it is to be feared that too many of parts and leisure, who live in Christian countries, are, merely through a supine and dreadful negligence, sunk into a sort of atheism.”

Berkeley indicts the Christian world of his time for gradually losing its Christianity and trending toward secularism and atheism. Such a secularizing tendency would become marked starting with the Enlightenment movement of the 18th century. This, for Berkeley, is a result of failing to see the clear evidence for religious truth that exists in nature and the growth of philosophical skepticism.

“For, after all, what deserves the first place in our studies is the consideration of God and our duty […]”

In the final paragraph of the book, Berkeley invokes the high religious purpose he had set for himself at the outset. As a philosopher who is also a clergyman, Berkeley sees as his mission to use reason to lead people to a contemplation of God and a moral way of life.