It is true, as Huxley says, that human beings would have made fewer mistakes if they had kept in mind their tendency to false judgments which depend upon extraordinary combinations of real experiences. When people say: I felt, I heard, I saw this or that, in 99 cases put of 100 they mean only that they have been aware of some kind of sensation the nature of which they determine in a judgment. Most erroneous inferences ensue in this fashion. They are rarely formal and rarely arise by virtue of a failure to use logical principles; their ground is the inner paucity of a premise, which itself is erroneous because of an erroneous perception or conception.[161] As Mill rightly points out, a large portion of mankind make mistakes because of tacit assumptions that the order of nature and the order of knowledge are identical and that things must exist as they are thought, so that when two things can not be thought together they are supposed not to exist together, and the inconceivable is supposed to be identical with the non-existent. But what they do not succeed in conceiving must not be confused with the absolutely inconceivable. The difficulty or impossibility of conceiving may be subjective and conditional, and may prevent us from understanding the relation of a series of events only because some otherwise proximate condition is unknown or overlooked. Very often in criminal cases when I can make no progress in some otherwise simple matter, I recall the well known story of an old peasant woman who saw the tail of a horse through an open stable door and the head of another through another door several yards away, and because the colors of both head and tail were similar, was moved to cry out: “Dear Lord, what a long horse!” The old lady started with the presupposition that the rump and the head of the two horses belonged to one, and could make no use of the obvious solution of the problem of the inconceivably long horse by breaking it in two.
Such mistakes may be classified under five heads.[162]
(1) Aprioristic mistakes. (Natural prejudices).
(2) Mistakes in observation.
(3) Mistakes in generalization. (When the facts are right and the inferences wrong).
(4) Mistakes of confusion. (Ambiguity of terms or mistakes by association).
(5) Logical fallacies.
All five fallacies play important rôles in the lawyer’s work.
We have very frequently to fight natural prejudices. We take certain classes of people to be better and others to be worse than the average, and without clearly expressing it we expect that the first class will not easily do evil nor the other good. We have prejudices about some one or another view of life; some definition of justice, or point of view, although we have sufficient opportunity to be convinced of their incorrectness. We have a similar prejudice in trusting our human knowledge, judgment of impressions, facts, etc., far too much, so far indeed, that certain relations and accidents occurring to any person we like or dislike will determine his advantage or disadvantage at our hands.
Of importance under this heading, too, are those inferences which are made in spite of the knowledge that the case is different; the power of sense is more vigorous than that of reflection. As Hartmann expresses it: “The prejudices arising from sensation, are not conscious judgments of the understanding but instinctively practical postulates, and are, therefore, very difficult to destroy, or even set aside by means of conscious consideration. You may tell yourself a thousand times that the moon at the horizon is as big as at the zenith—nevertheless you see it smaller at the zenith.” Such fixed impressions we meet in every criminal trial, and if once we have considered how the criminal had committed a crime we no longer get free of the impression, even when we have discovered quite certainly that he had no share in the deed. The second type of fallacy—mistakes in observation—will be discussed later under sense perception and similar matters.