Version: v1, Published online: 1998
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3. Hume and the reductionist project
Hume’s idea is that the ‘autonomous knower’ does indeed rely, and rely quite extensively, on the testimony of others, but does so because of constant conjunctions discovered by personal checking on their reliability in a testimony-free way. So Hume says of reliance upon testimony:
our assurance in any argument of this kind is derived from no other principle than our observation of the veracity of human testimony, and of the usual conformity of facts to the reports of witnesses. It being a general maxim, that no objects have any discoverable connexion together, and that all the inferences, which we can draw from one to another, are founded merely on our experience of their constant and regular conjunction; it is evident that we ought not to make an exception to this maxim in favour of human testimony, whose connexion with any other event seems, in itself, as little necessary as any other.
(Hume  1975: 111)
The idea turns out to be methodologically ambiguous: do the autonomous knowers accept testimony in an entirely piecemeal fashion because they have independently ascertained the reliability of this or that particular witness, or do they proceed by determining the reliability of the various classes of cognitive agents to which witnesses belong, or is it merely that they know they can do one or other of these checks if needs be? Given the scope and depth of our dependence on what others tell us, the first suggestion opens up our cognitive landscape to interminable investigative travelling that would make a nonsense of inquiry itself. The third asserts a mere possibility and hardly seems a move in the justificatory game. The second, which is more plausibly Hume’s idea, reduces the labour somewhat, but still requires an immense amount of checking, and more significantly owes us a non question-begging account of what counts as a class of witnesses. This is much harder to provide than it seems.
When Hume discusses the task of justifying reliance upon testimony, he talks at one point of its being ‘founded on past experience’ and varying in probity ‘according as the conjunction between any particular kind of report and any kind of object has been found to be constant or variable’ (Hume  1975: 112). But it is unclear whether ‘kinds of report’ are to be individuated by reference to type of speaker or type of content. If the former, then we are really checking upon expertise: we are seeking to find whether there is a high correlation between expert reports and the sorts of situations that experts report upon. But, even if we allow a broad interpretation of expertise (as we must if we are to include enough testimony for the project’s ambitions), we cannot detect expertise as we might detect colour or smell. That someone is an expert on the geography of Southeast Asia is either itself known in ways that rely directly or indirectly on the testimony of others, or it must be determined by observing personally some very high correlation between their reports and the state of the world. If the former, then we are no further advanced on the reductionist programme since the same problem arises over and over again; if the latter, then not only does the notion of an expert no longer provide us with a specification of a kind of report, but we would usually have to be experts ourselves to be in a position to determine whether the particular correlations obtain. On the other hand, if we interpret ‘kinds of report’ as ‘reports of kinds of situation’ we face other intractable problems. For instance, a problem arises immediately about the degree of specificity to be attached to the classification of kinds of situation. For the purpose of checking do we classify the utterance ‘This is a car that is in perfect working order’ as an existence report, a motor vehicle report, a mechanical report or an evaluation? There seems no intrinsic reason to proceed one way or another here, and yet it seems to be of the first importance how we go.
Coady, C.A.J.. Hume and the reductionist project. Testimony, 1998, doi:10.4324/9780415249126-P049-1. Routledge Encyclopedia of Philosophy, Taylor and Francis, https://www.rep.routledge.com/articles/thematic/testimony/v-1/sections/hume-and-the-reductionist-project.
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