Tuesday, September 03, 2002

Two Items: (i) Deduction, Induction, and -?-duction; and (ii) Important New (2001) Book


Item #1: Do we all now agree that 20th century American legal scholars in Evidence got it only half-right -- or 1/3 right -- when they said (characteristically) that factual inference involves induction rather than deduction? I think there are at least two things wrong with what they said.

Consider the simpler point first: Factual inference typically involves more than deduction. But it is quite incorrect to say that factual inference does not involve deduction. I'm right, no? Consider an astrophysicist who is drawing an inference about the location of Jupiter at 03:24 Greenwich Mean Time (or sidereal time?), June 13, 1827. This astrophysicist, in drawing his or her inferences -- in reaching conclusions about that question --, will certainly reason deductively on occasion -- by reasoning from, for example, Kepler's laws (as modified by Einstein's special theory of relativity?). It would not be difficult to find other such examples of the use of deductive reasoning to draw inferences about terrestrial phenomena (by, e.g., the use of the "laws" of chemistry, physics, or other such "hard" sciences). So we ought to correct our venerable predecessors (in the law of evidence) by saying that factual inference ordinarily involves more than just deductive reasoning.

But isn't there a more fundamental sense in which our predecessors -- legal scholars in the field of Evidence -- got at only part of the truth about factual inference? "Induction" means various things. But suppose we take it to mean an "inference about classes of events by the observation of particular instances or phenomena" -- or, if you prefer, the "extraction of general laws or general descriptive principles from the behavior or attributes of particular instances, events, phenomena, or data." If this is (roughly) what the problem of induction is all about, very little of the process of factual inference in forensic environments -- e.g., in trials -- involves this sort of reasoning. Although (as I have just suggested) proof in trials may involve the deployment or application of "general laws," factual proof at trial only infrequently seeks to divine or establish "general laws" that govern (selected) natural phenomena. (But it must be said that the process of proof in litigation sometimes is directed -- at least in part -- at establishing precisely such things, i.e., general {natural} laws, e.g., laws or principles that describe the relationship between certain types or classes of cancer and certain types or classes of sugar substitutes or, say, asbestos fibers). In many instances, however, the objective of forensic proof will be merely to "prove" -- to induce the jury to infer -- that a particular event happened and to do so by drawing on pre-existing general principles of some kind, ones that were not established in the lawsuit or trial at hand.

I suppose I'm saying the obvious. But if what I'm saying is so obvious, shouldn't judges should stop parroting the cliche (note: accent over the 2d "e" here) --, shouldn't they stop saying that factual inference involves induction rather than deduction? Folks who say that sort of thing are speaking -- at best -- 1/3 of the truth! {Ah, sometimes numbers just don't allow a person to speak very precisely!}

Item #2: Perhaps most of you are already in the know. But -- just in case -- let me say that students of forensic factual inference should be aware of the high praise that has been bestowed on a recently-published book: James Franklin, THE SCIENCE OF CONJECTURE: EVIDENCE AND PROBABILITY BEFORE PASCAL (Johns Hopkins University Press, 2001).

Shall we read this book together and talk about it?




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