I recently read David Hume's "Enquiry Concerning Human Understanding" in its entirety and wow, did it pack a punch. I only read pieces of it in college and didn't have the same familiarity with philosophy as I do today, so I couldn't appreciate it as much as I do now. It's clear why it's a must read for anyone interested in philosophy, particularly metaphysics. In such a short book, Hume does such things as establish an influential empiricist epistemology, found the compatabilist school of free will, and torpedo religious dogmatism. It's also very readable for anyone who took a couple of intro philosophy courses. The following is a reaction to a couple of aspects of Hume's work.
1. On the Origin of Ideas and Necessary Connection
Hume establishes his empirical epistemology by arguing that all ideas get their source from experience. Even with concepts that are not in their entirety found in experience,such as a unicorn, the parts of such a concept come from experience (in this case the horn and the body of a horse). This strikes me as correct, however, this point seems to undermine another. Hume makes the case that "necessary connection" is not found in experience, as any event that follows another can conceivably not occur. (It's conceivable that a ball remain suspended in the air when dropped; we know this won't happen only from experience.) Given the epistemology, Hume dismisses necessity as a legitimate concept, unless necessity is concieved as meaning "constant conjunction".
I would respond, however, that the position that ideas come from impressions in experience seems to rest on a kind of necessary connection, though perhaps not strictly logical. Would Hume confirm a "looseness" regarding the connection between experience and ideas as he does with the connections found within our experience. Though it may not contradict logic that ideas can come from something other than experience, there seems to be a deep connection between the two, though I'm not sure about the precise nature. It is the strength of this connection that Hume's empiricist epistemology is largely founded upon, thus creating a tension between his two points.
That being said, it may be the case that Hume's point about the "looseness" or lack of "connection" between phenomenon may be under-appreciated in light of modern physics. If I understand correctly, at bottom, the rules that govern atoms are time symmetric (can be run both forwards and backwards), but on the level of the day to day, events are manifestly time asymmetric. (Eggs crack and yolk spills out; yolk doesn't come together and return to the egg). However, this apparent asymmetry is only a matter of chance, since if the atoms happen to move in the correct order, events like yolk forming into an egg could happen, though with only a very low degree of probability. This statistical atomic movement is the basis of the Second Law of Thermodynamics, which states that entropy or energy dispersal (practically) always increases in a closed system. States of high entropy and low entropy, however, are in fact merely states of higher likelihood and lower likelihood of atomic arrangements (Using the egg example, a whole egg has a lower entropy and a splattered egg has higher entropy). Thus, according to physics , the causal relations we see in our day to day experience is not reflective of necessary connections, but rather the statistical probabilities of atomic arrangements. I'm not sure exactly what to make of this apparent corroboration between Hume's observations and modern physics, but I find it striking.
2. The Problem of Induction
What has been called the "Problem of Induction" is perhaps the most commentated on legacy of the Enquiry. Given that necessary connection isn't found in experience, Hume asks what is the rational basis for believing that similar appearances would have similar powers and that the future would be like the past.
He gives the example of bread and how it has "secret powers" in contributing to the nutrition of humans. However, these secret powers, can conceivably not exist in the next piece of bread we eat, as these secret powers are not found in the concept of the appearance of bread. Why should we expect that when we eat our next slice of bread, it shall have these secret powers.
I would like to note that given Hume's empiricism and the fact that towards the end of the book he dismisses excessive skepticism as unhelpful, I don't think Hume meant to create a puzzle for generations of future philosophers to solve. A point he did want to make, however, was the importance of "custom" or natural inclination in our behavior. When people postulate some metaphysical view like theism or idealism to justify induction, they miss this point. Hume points out that animals and babies act on the principle that the future will be like the past and similar appearances will have similar powers. Are animals and babies consciously aware of a metaphysical principal that would permit them to act this way? Of course not. These actions are automatic and instinctual.
That being said, I don't think that because there is nothing strictly in logic that would justify induction, it is rationally groundless. I think the rational ground is essentially the Principal of Sufficient Reason (PSR for short), which is "If something is one way, rather than another, and it doesn't necessarily have to be the way that it is, there must be an explanation for the way that it is". Take the bread example again. If we affirm PSR, then there is an explanation as to why bread has these nutritional powers. Likewise, if there is a piece of bread that does something entirely different, such as turn our skin pink, there would have to be a new explanation formulated for this new phenomenon, which has replaced the old (nutrition). However, if every piece of bread resulted in vastly different results, the PSR would essentially be a vacuous principle given the narrowness of any explanation and ,even more fundamentally, the impossibility of discovering any explanations. This impossibility stems from the fact no explanation could be subject to any predictive test.
Essentially, the possibility of induction is based on the assumption of the intelligibility of what we called the world. In other words, the assumption is that the world is explicable. Though this assumption isn't grounded on pure logic, it isn't necessary for it to be justified in order for it to be rationally affirmed. In fact, as Hume actually implied, it's a presupposition of the possibility of justification (at least regarding non-conceptual truth). It is a prime example of what Reformed Epistemolegists call properly basic beliefs, beliefs that are rational but do not have arguments for their truth.
3. On Miracles
I actually don't have much to say on this section, mostly because I find its principle argument to be sound; however, I would like to say I found it downright amusing. It was written during the first half of the 18th century and yet it sounds like something written by one of the New Atheists. At one point it sounds like a comedic routine. ( He essentially asks " Did you ever notice that as you read the history of nations, miraculous events seem to dwindle as you arrive towards modern times, at which they virtually disappear?). I am not surprised that this section was so controversial as to prevent him from having a university post. I am surprised the reaction wasn't even stronger considering that he wrote that religious beliefs aren't meant to withstand the scrutiny of reason, but rather are merely articles of faith. This is considered harsh even today. As a non-believer, though, I just found it funny.
