Stunned by the sudden, unexpected feint, Ambrogio can only try to stop me by landing a kick on my standing leg. That it is a foul there is no doubt, that it is intentional too, but the contrite and downcast look on my friend's face at the end of the match, forced to resort to such means given my well known generosity, moves me to an eccentric attempt at consolation. My companion's brain certainly works better than his feet, and over the post match "pizza", at a secluded table, I try to steer the conversation onto an abstract and reckless plane: his ungainly kick, I observe, did occur, my pain in the shin and my fall to the ground did too, but can one not perhaps doubt the connection between the two, which is, after all, the reason for his remorse?
On the "cause/effect" relation, as our chat thus begins, philosophy has always speculated, even devising the most abstruse questions: the kick (c) causes the painful injury to the shin (e) and so on, but what are c and e, events or facts (and what difference is there between the two)? Are c and e facts or single events or a process? What of probable causes? Are causal processes discrete or continuous? Are abstentions causes too (the government's failure to act caused thousands upon thousands of unemployed)? Is cause a transitive or intransitive relation, if a causes b and b causes c, does a cause c? And so on.
With Ambrogio we skip over the whole mass of questions and focus on one alone, the one that most directly concerns his misdeed: does the causal relation, we ask, exist or not? As real and concrete as the kick and the metamorphosis of my shin, is there also the causal link between the two? I mean: is it really there, independently of whether we are aware of it or not, independently of the human being and of mental activity? If it is there, if it is not a projection or a construction of the human mind, declaring oneself in short a realist, causality ought to belong to the ontological inventory of the world, as concrete as the stars, the atoms, and Ambrogio's intention that would have produced the painful consequences.
Embracing the realist conception, apparently that of common sense (and above all of science), and granting in general that relations exist (some doubt it), we ought in some way to have experience of causality. I should be able to ascertain in some way that the movement of one ball produces, brings into being, creates, all synonyms of "cause", the movement of the second. Of course, science, physics in particular, will later teach that the true causal factors are quite other than the macroscopic kick and shin, but without the initial news that the link holds, without starting point checks, how then are we to suppose that the relation dwells in the entities of the world that we infer and do not directly observe? How can we not think that causality is the fruit of some imagining or of our mental structure, useful perhaps but imaginary all the same?
In high school we learned that a famous anarchist thinker, around the middle of the eighteenth century, casts doubt on whether that original experience, at the base of all the knowledge that follows from it, is simply there at all. In the history of philosophy David Hume (though the sceptics had already put forward his doubt) appears as an irreverent urchin who, among a whole population of children celebrating every year the imminent arrival of Father Christmas, one fine day speaks up and says: no!, Father Christmas does not exist, explaining also why we believe he exists. As often happens in such cases, heated protests break out, but then, little by little, first a few and then many begin to doubt he is there. Even if someone keeps saying he sees him, the enchantment is suspended.
Hume observes that, to be sure, in a billiard ball striking a second one, we always see first the first ball moving toward the second, then the two balls touching, and finally the second one moving. But this means that experience testifies to the succession of a certain kind of phenomena, to their contiguity and their regularity, and to nothing else. Hume was certain that the world would go on this way and that, had he ever witnessed, in the same kind of situation, the second ball remaining still when struck by the first, he too would have begun to believe in ghosts or in occult forces (causal ones all the same). This does not alter the fact that the reason for such astonishment is, in his view, walled up in our head, in the habit of a world that invariably behaves, that has so far behaved, in this way. Reality, the one shown by experience, even if the second ball, all conditions being equal, did not move, which has never happened, would offer no reason for perplexity. As if to say: precisely because there is no cement binding the phenomena, none is manifest, if one kind of regularity were replaced by another, or if the regular course vanished altogether, there would be no need of any explanation of the change. If the regularity of the world presupposes nothing else, then any irregularity too should be accepted as a gift of fate. Hume certainly did not imagine that brains as eccentric as his own would later call into question even the experience of "succession" (the perception of time) and of "contiguity" (the perception of discrete events), which he accepts; this does not alter the fact that he deserves a place of excellence among those who, after generations upon generations, call into question something previously held to be entirely obvious.
At first glance it seems that, if the Scotsman is right, since mere intentions do not constitute a crime, the kick willed by Ambrogio is not chargeable. The blow to the shin did, alas, follow, but one certainly cannot say that it was he who produced it for me. Yet then one comes to think that, juridically, nothing changes: since intentions, like the rest of the world, never cause, in judging willfulness and liability one will have, obtorto collo, to make do only with the regularity of events. Can you imagine two footballers trading kicks, punches and shoves, following each act with the excuse that it was the world that turned the intention into fact?
Various objections have been and are raised against Hume. To begin with, the one according to which experience testifies, it is insisted!, to the causal relation. Here we are at loggerheads, where to one who sees another who does not see replies. But in what sense, one may ask, does one not see? And if one does see, why lie? How often does the denial of the obvious withdraw the obvious from circulation? The busillis that the Humean apostasy drives into our head might take the form of a sincere question to put to oneself: what, properly and specifically, do we see or touch or experience when we witness a causal relation?
Among the many objections to the Humean heresy, then, let us choose two or three of the better argued. Suppose I am allowed to break, with an Inter football, a pane of glass in front of me, indeed that with the same ball thrown at the same speed, with equal air resistance, I could break 10 or 1000 panes of the same thickness and material. Then I repeat the same operation with a Milan ball, then a Roma one and so on, all of weight and dimensions identical to the Inter one but of different colours, until I tire of it. It seems evident that the colour of the balls, however much faith one may have in the strength of a team, is entirely indifferent to the breaking of the glass; this depends, at least macroscopically, on the weight and speed of the ball, on the thickness of the glass, on air resistance and so on. How then can one deny the existence of causal links? At this objection Hume would probably not have batted an eye. If he is right the conclusion does not follow, and it does not follow at any level, neither that of three-dimensional objects nor that of elementary particles. However many experiments with differently coloured balls are carried out, the answer that experience testifies to is the following: the day before yesterday the panes were broken with the Inter ball, yesterday with the Milan one, today with the Roma one, and so forth. To be able to distinguish determining factors from superfluous ones, I should be able to say that, using the Inter ball, even "had I used the Milan one", the glass would have broken just the same. Which, among other things, suggests that common sense and science do not merely observe the world. Without mental journeys into the possible, and the distinctions such journeys allow, regularity stops at Hume's laconic experience, at the regular series. But once the causal relation is struck out, it is precisely the hypothetical clause that becomes arbitrary. If and only if certain factors show themselves to be causally determining and others superfluous do the former justify the hypothetical clauses. It is at the very least rational to suppose, if causal links appear and assuming they are necessary and sufficient, that had causally determining facts or events not been present the glass would not have broken, and that were they present the panes would break, which does not happen with colours. But for Hume no causal links are to be seen.
In fact some philosophers, convinced like Hume of the inscrutability of the causal relation, hold that one can do without the phantom metaphysical glue, keeping the idea that the regular sequence occurs only with certain factors and not with others, thus saving all that the old causality told us about the world, and with it the capacity of common sense and of science to "latch onto" and explain reality: it would be a sort of surrogate for causality that retains its qualities while abandoning the fictions. As if to say: a pollack indistinguishable in flavour from caviar. If the supposed causal relation, so the reasoning goes, reveals that "if it is true that c", then "it is true that e" (and that "if it were true that c is absent" then "it would be true that e would not be" and so on), it is enough to assert the truth of such conditionals, called "counterfactuals" or "subjunctive conditionals", without thereby also having to maintain the causal relation. In short, I posit virtual truths alongside actual ones while abandoning the links between their referents. Against the reduction of causality to subjunctive conditionals various objections are raised, imagining cases in which it would not work, but the impression that it goes in a circle is the one mentioned above. If Ambrogio's kick causes the bruise, it is legitimate to think that, all conditions being equal, had he not given it to me I would have dribbled past him, and that were he to give it to me I would crash to the ground, as in fact happened. But if the causal relation is not there, on what basis do I assert possible truths, from what do I set out to justify them? What guarantees the journey into virtual reality? It really does seem that the reduction of causality to counterfactuals sets out from the possible to arrive at the real. A cart pulling the oxen.

Another objection, by contrast, really does throw Hume's doubt into crisis, though indirectly. We started from the realist idea that experience can reveal a world existing independently of us. Hume believed that we have experience of our own sensations ("impressions") and not of the world, but when he reduces cause to empirical regularity he cannot do without the world. If the world produces, causes, sensations in me and these are attributed to objects or events, then I can assert that certain successions of phenomena do in fact present themselves in a regular way. But if the world does not modify me by producing the sensations (which I attribute to it), I do not even have experience of regularity. It is enough that, in seeing the two billiard balls, I move a little closer or farther or shift even slightly for the images I observe to be not at all the same and to form no regularity, whereas the whole Humean dispute starts precisely from phenomenal regularities. Hume therefore, despite himself, does not describe "sensations" but "objective phenomena", and to describe these the images we have must be of objects of the world, so that these at least produce in us the sensations that concern it. If the world testifies only to regular series without presupposing its causality, we do not even arrive at that testimony. Among other things, it is precisely from the impact of the visible world that we can infer the invisible world and the strange entities of science.
One last rejoinder. Ambrogio's treacherous kick had the effect it had. It is also true that we often perform actions without reality changing one et. If I mean to stand up and someone begs me to remain seated, an invitation I accept, I do something without causing anything. Abstentions too, like positive actions, obey imperatives. But in all actions that are not abstentions, and without which the latter would not even be known to us, if my action has no volume, if it does not bring about something in the world, it seems it is not there. The intention to go to the seaside this summer would be an action just like going there. As if to say: if an intention in action brings about nothing, how are we to distinguish the actual action from the mere plan to act in the future? If both are mental episodes that have no effect, how do I distinguish an action (a positive one), something I do, from something I do not do? Certainly, up to now, usually, to the intention in action there corresponds some change in the world, even in attempts that come to nothing, but without causal glue and counterfactual conditionals, that correspondence does not concern my actual acting, does not explain it and make it possible; besides, the correspondence has all the air of a mystery.
The pizza and beers are finished and Ambrogio, engaged until now, sums up the outcome of these musings. If what has been said so far makes any sense, it follows that: a) the concept of cause ought to derive from a certain experience we have of it. If it does not in some way depend solely and only on the mind (whatever the latter may be!), as a real, primitive and irreducible relation, causality cannot be inferred or derived from anything else. And on the other hand it can be doubted that we have experience of it. The very fact that for some the experience is there, for others not, tells against its self-evidence, and perhaps it is also problematic to grasp what it means to have "self-evidence" of it. And yet b) not only, without causality, do common knowledge and science seem to go to the dogs, both in the sense in which the latter aspires to knowledge of the world and because the passage from the visible to the invisible becomes a leap in the dark, but we could not even content ourselves with describing the blessed "regularities". Regularities without which knowledge amounts to a fistful of (imaginary) flies. Mere images of flavours, colours and smells christened by my mind, who knows why, "ham pizza"; properly speaking, I have not even "cut" and "eaten" the pizza: the idea of pizza produces no flavours and that of a knife does not cut. So? What is the result of the chat? (And what of my kick? But this Ambrogio does not say.) Ruminations of this sort are worthy only of a fourth rate Azzeccagarbugli.
I agree. The discourse ought to go on and dissolve the casuistic and pettifogging tricks scattered so far. To dissolve them, at any rate, one needs a legal quibbler more precise and meticulous than Azzeccagarbugli. The fact is that my belly is full, I am tired, Ambrogio has grown distracted but not repentant and, above all, my shin aches. Better to postpone the continuation of the dispute to another occasion. Perhaps to the next match. Possibly without the deadly kick.

Luigi Cimmino teaches Gnoseology and Ethical Paradigms at the University of Perugia.