In his Enquiry Concerning Human Understanding David Hume investigates the processes by which we form concepts of the world and critically examines the validity and the limits of such understanding. One of the concepts that he examines in particular is our claims about causal relations. When I say that fire causes smoke, what am I actually saying and what can I actually guarantee by my claim?

The first thing that Hume says is that we must have experience in order to know anything about the world. He uses the example of Adam, seeing the world for the first time. What would he have known about the world, other than what his senses perceived? Could he have known that water will drown a man, just from looking at it? Could he have known what foods were edible, or even that objects could have the property of being edible or inedible? The conclusion he arrives at is that Adam would have known next to nothing about the world because there is no way to reason about an object without experiencing it and its effects in different contexts. Reason cannot act without experience.¹

Since we must use experience to inform us about the world, anytime I wish to reason about things I must essentially reason from my experience of what the world is like. For example when a person says that fire causes smoke, what he is really doing is examining his experience and finding that fire and smoke have always been conjoined. Whenever two events, states, or objects are conjoined in our experience, we tend to say that one causes the other. What Hume finds very interesting in this proposition is the fact that when the person sees this causal relation, there is in fact nothing that forces it to be the case. Technically, all the person can do is say "in my experience in the past, fire has always been conjoined with smoke". There is nothing inherent in the experiences that says that fire and smoke always will be together. In other words, there is no way to claim necessary connection. In essence when I make a causal claim what I am saying is:

1. In the past, x has been associated with y
2. Therefore, x will be associated with y in the future

There seems to be a step missing here, something that ties the two steps together. Hume says that what we are actually doing is implicitly assuming that the future will follow the way the past has been going, so that things that have happened in the past are likely to occur in a similar way in the future. If we assume that then we can reasonably conclude that x and y will occur together in the future. So now the reasoning looks like this:

1. In the past, x has been associated with y
2. The future follows in an orderly way from the past (the future resembles the past)
3. Therefore, x will be associated with y in the future

(The last statement can be reformulated as "x implies y")

Now that we have a framework with which to understand our reasoning, Hume begins to question the validity of making the assumption in the first place. It is possible to reason about it? Can we show that it is correct? Perhaps one way is to put the assumption into effect and see whether or not it is effective. If we reason about the world this way, do we make accurate descriptions and predictions? As it turns out, there is no way to prove this assumption because any experimental proof that one might bring relies on the assumption that if there is proof of something in the past, it will work in the future. We rely on the same assumption that we are trying to prove, and we end up begging the question. The next approach that one might take is to reason about this through the sole use of logic, trying to escape the trap that empirical induction leads us into. The trouble is that there is nothing inherent about the assumption that we can reason in an a priori form about. It could be true, or it may not be, but there is nothing in virtue of its form that one can decide about. Thus, we are left with an assumption that cannot be proved empirically, and therefore our reasoning about causal relations is not based on logic.

What Hume has done is shown that our reasoning about causal connection has no logical necessity and ultimately has no rational basis. Always present in our judgments is an unprovable assumption. This is not to say that we shouldn't go on reasoning about the world the way we have been, just that there is a limit to the powers of causal claims.

Node Your Homework

"Stuff just happens. What the hell."

-Didactylos


What goes up does not necessarily have to come back down. There is no reaction for every action. Stuff just happens, and does not need anything to make it happen. This is one of the tenets of David Hume's skepticism, which states that not only is effect not possible to determine a priori, but does not, in fact, exist at all outside of the habits of the mind. This argument, as he constructs it, is elegant in that it makes a bold point with supportive evidence and no easy refutation. This is as much a weakness as it is a strength, for clever wording does not logic make.

The Strengths

Flip a coin. Do it again. And again, and again, and again. It always comes down, right? Doesn't matter. It will, eventually, not land heads or tails because, eventually, it will not come down at all. Cause and effect is an illusion, a habit of the mind to find order and workability in the world. "Tell a man a lie often enough, and he will eventually believe it."

First, knowing the effect a priori is impossible. "Present two smooth pieces of marble to a man who has no tincture of natural philosophy; he will never discover that they will adhere together in such a manner as to require great force to seperate them in a direct line, while they make so small a resistence to a lateral pressure." When we see an effect, we attribute a cause to it because we've seen the pattern before; A always happens right before B, so, therefore, A causes B. Not according to Hume, who says that nothing in this existence follows from anything else, and that anything that ever happens is a random event, and that what looks like cause and effect is nothing but a string of coincidences. Coincidences that happen all the time.

This is a very difficult argument to disprove, as both rational and empirical evidence is very difficult to find.

Empiricially speaking, to disprove Hume's arguments about causality, you would have to repeat an action endlessly, with the exact same conditions, for all time, with the idea being to find out every single possible series of events that make up that action. Needless to say, this is both impossible and inconclusive. So what if the coin lands heads every time? Doesn't mean it can't come up tails. We just haven't seen it do that yet. Flip it again. There is no way to empirically prove, beyond a shadow of a doubt, that C, instead of B, cannot follow A. It can't be done. Score one for Hume.

Next challenger...reason. You can fool an empiricist, but you won't get me! You say that one billiard ball, squarely and straight-on contacted by another billiard ball, will not always move ahead in a straight line? But, it always does, and, furthermore, everyone knows intuitively that it will. Interesting point, but...just because something always has happened, does not mean that it always will happen. Secondly, the billiard ball example is not a priori knowledge. Take a man, completely in control of his faculties and intelligence, who has been deprived of all experience of the Coincidences of Physics, and ask him what will happen if one billiard ball is shot with force directly at another billiard ball. He will not know, because he has never seen anything like it happen, and is thus unable to extrapolate from past experience. Next, take that same man, and place before him a pile of gunpowder, and ask him what will happen if he were to place a lit match into this anonymous grey dust before him. He won't miss those fingers. Now, once you've got him properly bandaged, take him to a deciduous tree in winter, and ask him what will happen when the days get longer and the snow melts. Again, he will not know. He probably also has a nice case of frostbite and hypothermia by now, as he does not think that the white stuff on the ground is only, and coincidentally, of course, around when the air is very cold.

And thus Hume stands strong. Even given an infinite timespan, there is no empirical way of proving that one thing will always follow from another thing. There is always room to object, to postulate other possibilities, and they cannot be discounted. You cannot disprove Hume rationally, either, as to do so always requires you to fall back on the assumption you're attempting to prove. Also, causality cannot be a priori, and therefore a rule, because a the effect of a cause cannot be predetermined without experience of some kind that allows the observer to predict or extrapolate what comes after an event.

The Weaknesses

There's something about Hume's argument regarding causality that strikes me as almost infantile. You can use to counter any argument with something like, "Well, just because the billiard has reacted that way every time it, or any other billiard ball, has been struck in exactly that way, doesn't mean that next time it gets hit, it won't spontaneously mutate into a howler monkey, give the bartender a wedgie and then solve complex trigonometry on an abacus before bursting into flames and melting back down into the 8-ball you've been trying to sink for the past half-hour, you jammy git." This can be done into absurdity, with absolutely no rational or reason behind it. Yes, the billiard ball could hook sharply to the left after being struck dead-centre by another ball travelling in a perfectly straight line, with no deviation or side-spin, but why would it do that? Oh, right, I forgot. Everything is nothing but a series of coincidences. Well, Mr. Hume, I'd say it's pretty unbelieveable that every time you concidentally made another mark on the paper right after you conincidentally made the previous mark, it coincidentally became a series of marks that coincidentally could be viewed by human eyes, and thus coincidentally cause thoughts that coincidentally were the same as yours to coincidentally occur in the minds of anyone who coincidentally happened to view it. Good thing you coincidentally made marks on the page that coincidentally were associated with you, else you might not have coincidentally gotten the royalty checks or the dinner invites. Good thing for you we all stupidly associate things together. The purely mathematical odds of an series of coincidences so high in number as to be called infinite all happening in the exactly correct sequence needed to create a species of life that is capable of rational thought and give them a suitable place to live and give them the ability to manipulate the tools and language they need to communicate so unlikely as to be called impossible. The odds in favour of it are so small as to be called non-existent. One, just one, coincidence gone the other way, and we'd still be in the damn trees. Hume has neatly shifted the burden of proof onto opponents to his arguments, which leaves them at a great disadvantage. Just because A cannot be completely disproved does not mean it is always true.

Now, flip a coin. Do it again. And again, and again, and again, and...what? The coin didn't come back down? My god, Hume was right! No, wait, look up. There's the coin. It's caught into the rafters. Now, with my magic reality-altering powers, I will remove the rafter from existence. Hey, look, the coin came back down! It would appear that the rafter was causing the coin not to come back down.

Well, it could be a coincidence that the coin was caught in the rafter. It could be a coincidence that that billiard ball, did, in fact, make a sharp hook to the right. However, if you examine the pool table, you'll find that the table's slanted and there's debris on the surface, thus deflecting the course of the ball. But, can it be a coincidence that anything exists, anywhere? If we look around the world, it cannot be denied that there appears to be a cycle of creation, degredation and dissipation. The tree grows from a seed into a mighty tree, then dies, collapses, and rots into soil. That cannot be denied. But where did the world come from? Where did the star system, the galaxy, the universe, the very fabric of existence itself! It is too large, too varied and too complex to have come from mere coincidence. Something, if you regress back far enough, started the whole process, whether it was God or a Big Bang, and thus is was a cause, and it had the effect of bringing existence into being. Even if there was no more causality after that, it if happened once, it can happen again, and therefore it exists.

For proof of causality, one must only look at ourselves and our environs. Complex structures, whether biological or physical, cannot, mathematically and logically, come from a series of coincidences. First, our solar system is exactly set-up to support and protect our species. The planet is exactly the distance away from the sun to support life. The moon is of exactly the right size and distance to effect the tides, giving us the varied ecosystem required to create an atmosphere and food-chain that will support life. There are exactly enough planets and debris in the outer solar system to protect this planet from radiation and debris, as we saw several years ago when Jupiter's gravity well pulled in several asteroids that would otherwise have collided with the Earth, ensuring the extinction of all life on this planet.

Next, the sheer diversity of life, the thousands upon thousands of species of plants and animals that all work together perfectly in a balance that exactly maintains the breathable atmosphere and food source. Our brains are exactly wired to have sentient thought, our bodies are composed of billions of cells that all interact exactly (we hope) in the manner needed for us to live and function. All of that, all of those trillions of interactions in one organism, every second, all a series of coincidences? Once again, the odds against it...inconceivable.

Finally, take our example man and place him in a controlled environment, say a tall, sealed room where there is no wind, constant, unchanging gravity. It's a controlled environment. Now, while this hapless test case is standing at the bottom of this room, drop an oversized 50-ton weight (a la Bugs Bunny) on his head. Our test case has now been reduced to a thin smear on the floor, walls, weight, and whereever else he managed to splatter. There is not one single human being who will not do the exact same thing when the weight is dropped on their head, again assuming a controlled environment. Thus, if it is guaranteed to happen 100% of the time, it is no longer a coincidence. And if there is one, just one, case where A causes B, then cause and effect do exist.

The Kill

While highly elegant and well-written, not to mention thought-provoking, Hume's arguments on causality, under closer scrutiny, are shown to be highly elegant, well-written, and lacking in any real, rational, substance. It is an argument that can never truely be disproven, but it can be dismissed on logical and mathematical grounds as absurd and ridiculous, making about as much sense as an 8-ball mutating into a noisy, left-brained simian with a prehensile tail and a taste for slapstick comedy.

Even if every event B that appears to follow from event A has a 99.99...% chance of occuring as event B, that means, but simple mathematics, that event C will occur 0...1% percent of the time, and, given the well-nigh infinite number of events that occur every second, and given a controlled environment (i.e. a lack of Infinite Improbability Fields, rocks on the pool table), that means event C will happen very frequently. Which it doesn't. (It should be noted here that the Argument from Design essentially disproves Hume's arguments on causality, yet he defends that same Argument in Dialogs Concerning Natural Religion. Hmm.)


The pipe is my friend.

Some philosophers such as Peter Strawson deny the problem of induction. Strawson uses what is known as The Ordinary Language Response to claim that it is not in fact a problem at all.

Strawson claims that to doubt that relying on induction is "reasonable" is nonsensical. It is an Analytic truth that induction is reasonable. An example of an analytic truth is “A bachelor is an unmarried man”, we know this to be true as the definition of "Bachelor" is "An unmarried man".

In the same way, When we use words like "reasonable" and "justifiable" we mean: "Capable of being reasoned" (using inductive methods). When we claim that a scientific theory is "justifiable" we mean that it has been established based on an appropriate number of observed instances (i.e. using induction) . The way we ordinarily use the word "reasonable" includes the idea of inductive reasoning.

Thus, asking "Is induction reasonable?" is a confusion in a similar way as asking "Is the law legal?".

Strawson's argument is tempting because, as Bacchon points out, the problem of induction is annoying. We feel that Hume is wrong in some way but his argument doesn’t seem to have any major holes in it. We really just want a way to sweep it under the rug and get on with our lives and the ordinary language response works for this, “Ok, so maybe induction is a flawed way to go around determining stuff. But it’s close enough to common sense, in the way we usually use the term “common sense”.

But it’s still pretty obvious that the response sidesteps the problem, rather than solves it. The sceptic can just rephrase the problem of induction without using “immune” terms like reasonable or justified.

And also, you can try using Strawson’s argument to justify all kinds of fallacies. Suppose you were to find a community who consider “wishful thinking” to be a good way of establishing the future? With this communities linguistics wishful thinking would be perfectly “reasonable” by their definition of the term.