Book Summaries Philosophy

An Enquiry Concerning Human Understanding Summary (8/10)

An Enquiry Concerning Human Understanding by David Hume is considered one of the most philosophical and scientific texts ever written, and primarily, it exposes the limits of human rationality through a series of 12 essays that are quite rational themselves.

Indeed, Hume starts by admitting to the limited power of his own arguments, but in the end of the book, he makes it clear that one cannot be skeptical of everything since it would hinder our ability to function in the world. Instead of disposing with rationality altogether, it would be wiser to find out which areas of knowledge are dependable and throw out the rest.


“Man is a reasonable being, and as such, receives from science his proper food and nourishment: But so narrow are the bound of human understanding, that little satisfaction can be hoped for in this particular, either from the extent or security of his acquisitions.”

All the perceptions of the mind can be divided into two classes The first is impressions and the second is thoughts or ideas. The first can be distinguished by their different degrees of force and vivacity. When have impressions of the world, these are either good or bad.

“By the term impression, then, I mean all our more lively perceptions, when we hear, or see, or feel, or love, or hate, or desire, or will.”

After repeated impressions, we form relations between different events in our minds. Either they are like something we remember, or they appear to have caused or have been caused by it. But absent experience, we have no way of predicting future outcomes. And even if we could predict future outcomes based on experience to a certain extent, we have no real insight into why these outcomes were caused.

Hume makes a distinction between matters of fact (it will rain this winter) and relations of ideas (a triangle has three sides).

In the same way a dog learns through repeated behavior, humans can only learn through repeated exposure. The difference between humans and animals is only a difference in degree, not in kind. Without experience, we have no way of discerning between accurate and inaccurate truths.

To understand his argument, think about a billiard ball on course to collide with another one. If we had just appeared in the world, through time travel from a different galaxy, to see this event, we would have no way of predicting what would happen – there is no logical way of knowing. Rather, it is only through repeated exposure that we make the causal connection between the two events, but this causal connection is not a necessary connection. That is, it is conceivable that the ball that is hit will follow a different direction from the one we anticipated.

If we concern ourselves with matters of fact and relations of ideas, then we would be able to function properly in the world. But anything that is metaphysical in nature, that has no numerical value associated with it, that cannot be disproved, and that is highly speculative, only serves to mislead us.

“The academics always talk of doubt and suspense of judgment, of danger in hasty determinations, of confining to very narrow bounds the enquiries of the understanding, and of renouncing all speculations which lie not within the limits of common life and practice. Nothing, therefore, can be more contrary than such a philosophy to the supine indolence of the mind, its rash arrogance, its lofty pretensions, and its superstitious credulity.”

Our metaphysical thoughts are so weak that they are not worth relying on at all. Our weakest impressions of the world are more powerful than our deepest thoughts. Even matters of fact, that are observable (through repeated behavior), are not things we can depend on (It might not rain this winter).

When a pattern of behavior is repeated enough, we know that it is highly probable that the event containing the billiard balls will unfold in the way we expect. And that is how it works with everything else in life. We see events happen in conjunction very frequently, and we make the logical leap into associating them as cause and effect. But since this connection is not necessary, then we are able to solve an important moral dilemma.


Compatibilism is a philosophical idea that states that it is possible to have free will in a deterministic universe. First, imagine the world was deterministic: every cause has a necessary effect.

Now think of this scenario.

A man was convicted of murder and we want to know whether he should be punished. Assume also that we had perfect knowledge of their history (biological and environmental). If we lived in a universe where events had a necessary causal connection between one another, then we could state confidently, that this man’s act of murder could have been predicted. In which case, it is difficult to convict him of anything since he had no more of a say in the matter than he did to belong to this world, or to be born of his two parents, or to be a man and not a woman. But Hume’s argument allows us to escape this conundrum.

If there is no necessary connection between events, then this man could have acted differently. He had the freedom to choose, even though the series of events that preceded his murder largely did determine his will to do so. That is because the determinism here is probabilistic, but not absolute. There is no set of preconditions that could have forced him to murder his victim no matter what.


Hume explains limitations of reason before proceeding to the subject of miracles, which according to him are against custom or our own experiences of the world, but we should be reminded of the limitations of these experiences– we don’t have much of them. If we rely on custom, then the amount of data we are drawing on is too limited. And, since our reason is limited, we cannot judge a priori whether miracles have or have not occurred. Hume himself would admit to this limitation, so a push for atheism, on this basis, is weak at best.

But his argument here is simpler than that, and much less ambitious. If someone attests to a miracle, it is highly probable that they were delusional or mistaken than it is the case that the laws of nature were broken. If you were standing before a judge and claimed to witness the laws of nature being broken, you will need to present evidence that is so strong, that the idea of you being wrong is more incredible than the idea that the laws of nature had been broken. The judge will then look at the two positions, one that the miracle did happen and the laws of nature were broken, and compare the weight of this evidence against the latter position – that the miracle did not in fact occur, and that the witness is either lying, delusional, or mistaken.

Further, when contradictory claims about these miracles is heard, this makes it even more difficult to believe that the miracles occurred since each contradictory position requires the plaintiff to present even stronger evidence to support their claim (since there is more weight on the other side of the argument). This makes it more difficult to believe in religious accounts, whether Christian or Islamic, about the existence of supernatural events. But Hume also reminds us, that it is unfair to attack religion based on rationality and is unwise for proponents of religion to base their belief on rationality (or on miracles for that matter). Religion is a matter of faith, and that is what makes it a religion. It is the willingness to believe, despite having no reason or evidence. Hume is not attacking proponents of religion; he is attacking proponents of religion who seek to use rational arguments to justify their belief.

“To make this more evident, let us examine those miracles, related in scripture; and not to lose ourselves in too wide a field, let us confine ourselves to such as we find in the Pentateuch, which we shall examine, according to the principles of these pretended Christians, not as the word or testimony of God himself, but as the production of a mere human writer and historian. Here then we are first to consider a book, presented to us by a barbarous and ignorant people, written in an age when they were still more barbarous, and in all probability long after the facts which it relates, corroborated by no concurring testimony, and resembling those fabulous accounts, which every nation gives of its origin. Upon reading the book, we find it full of prodigies and miracles. It gives an account of a state of the world and of human nature entirely different from the present: Of our fall from that state: Of the age of an, extended to near a thousand years: Of the destruction of the world by a deluge: Of the arbitrary choice of one people, as the favourites of heaven; and that people the country-men of the author: Of their deliverance from bondage by prodigies the most astonishing imaginable: I desire any one to lay his hand upon his heart, and after a serious consideration declare, whether he thinks that the falsehood of such a book, supported by such a testimony, would be more extraordinary and miraculous than all the miracles sit relates; which is, however, necessary to make it be received, according to the measures of probability above established.”

"Silence is the best expression of scorn" - G.B. Shaw

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