How to define levels of explanation and evaluate their indispensability

Some explanations in social science, psychology and biology belong to a higher level than other explanations. And higher explanations possess the virtue of abstracting away from the details of lower explanations, many philosophers argue. As a result, these higher explanations are irreplaceable. And this suggests that there are genuine higher laws or patterns involving social, psychological and biological states. I show that this 'abstractness argument' is really an argument schema, not a single argument. This is because the argument uses the 'is lower than' relation, and this relation admits of different readings. I then suggest four rigorous definitions of the 'is lower than' relation, and show that the abstractness argument's prospects are much brighter for some of these definitions than for others. To show this, I evaluate the so-called 'disjunctive threat' to the abstractness argument. Some explanations belong to a higher level than others. To a very rough approximation, psychological explanations are typically higher than physiological ones, for example; but psychological explanations are typically lower than social ones. And so, for any explanation that correctly explains why a phenomenon occurred, one can ask: is there some lower explanation that also correctly explains the phenomenon? And, if there is, can this lower explanation replace the higher explanation? And by 'replace' I mean: the higher explanation provides no understanding (of why the phenomenon occurred) over and above the understanding of it that the lower explanation provides. In practice, philosophers agree that the answer is often that the higher explanation in question can't be replaced. Suppose-just to explore how absurd the idea is-that every correct higher explanation could indeed be replaced by some correct lower explanation. This would in many cases require that the lower explanation describe monstrously complicated lower facts. Instead of describing a nation as being atwar, for example, it would need to describe the actions performed by each of several thousand soldiers, civilians and politicians. But human inquirers are not able to entertain such monstrously complicated propositions, let alone communicate such propositions to others. Thus some higher explanations are irreplaceable-at least 'in practice' for human inquirers. Much more controversial, however, is the question of whether some higher explanations are irreplaceable even 'in principle'. 1 On the face of it, this question seems to be a question about an idealizer inquirer, one who can entertain more complicated propositions. The question asks: do any higher explanations provide this idealized inquirer with understanding above and beyond that provided by every lower explanation? Unfortunately, this question doesn't specify the extent to which one is supposed, when tackling this question, to idealize away from our cognitive imperfections as humans. Exactly what propositions is an idealized inquirer supposed to be able to entertain? As a result, there is a risk that the controversy over in-principle replaceability will boil down to an insubstantial dispute over the definition of an idealized inquirer. This paper will clearly identify the substantial issues at stake in this controversy, and will separate them from insubstantial disputes over definitions. Specifically, it will clarify the logic of an argument at the centre of the controversy, which I will call the 'abstractness argument'; and it will clarify the logic of the so-called ` disjunctive threat' to this abstractness argument. For one thing, I will show that the abstractness argument appeals to an ` is lower than' relation that admits multiple definitions. This is important because it is easier to neutralize the disjunctive threat to the abstractness argument for some definitions of the ` is lower than' relation than for others, Iwill show. For example, I will show that the abstractness arguments run by several philosophers fail-namely those run by Block, Fodor, Kincaid, Kornblith, Levine, Marras, Pereboom, Putnam, Weslake and at one stage Antony. I hope that the clarificatory work of this paper will allow me to press this criticism more clearly and forcefully than existing criticisms in the literature.