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mination of a number of individual cases, in order to discover some common property or circumstance in which they all agree, amid many others in which they differ*.
Does then the process consist merely in this, that we examine every individual of a class, or number of objects before us, and, finding each one to possess a particular property, affirm that as a common property of the class? This, certainly, would imply no exercise of reasoning, and would hardly be worthy the name of induction. We should be merely affirming a proposition for whose truth we had the direct evidence of our senses. Yet perhaps among cases even of this sort, there may exist much difference as to the extent and labour of the research we may have to go through, in detecting the one property, which is common to all the individual cases, and constitutes the characteristic by which we give them a common classification and a generic name. The point in which all the examined instances agree, may, indeed, be manifest at first sight. But, again, it may be far otherwise; and though we have all the cases before us, (especially if they be numerous,) it may yet require no small labour and skill to succeed in tracing out what the property or circumstance is in which they all agree, amidst a variety of others in which they differ. The first case requires nothing further than the bare inspection of the instances.
* This "bringing in," as it were, of fresh testimony, and corroborating witnesses, was probably the original idea of "inductio,” or ἐπαγωγὴ.
The latter may call forth much discriminative skill. The former is the work of the mere collector: the latter may involve that of the philosopher. But in any case other than the most immediately obvious, there is this to be remarked; and it is deserving of particular attention: it is almost certain that, in the first instance, the mind will conjecturally fix upon some property, which is imagined (whether correctly or not) most likely to be the common one sought, long before a complete examination of all the individuals has taken place*.
Let us suppose, on the other hand, that we have not all the individual facts before us. We observe a certain number of them, and finding them agree in some property, we are almost invariably prone at once to infer, that all the rest possess it likewise. We infer more than we see. There is certainly a strong natural tendency in the human mind (even upon very slight apparent grounds) to advance from individual facts to general conclusions, to hazard inferences from the known to the unknown.
Grounds of Inductive Conclusion.
We have then next to inquire with what reasonable confidence can we make such inference? For instance, suppose that feeling a number of balls in a bag, we take out a few, and, finding them white, infer that all the balls in the bag are white: is this a legitimate induction? Is it correct reasoning; is
* See Sir John Herschel's Introductory Discourse on Natural Philosophy, p. 165.
it not rather a most groundless presumption? Yet it may be asked, does it not possess all the characteristics of induction, as they have been laid down by some logical writers? For wherein does the case we have supposed, differ from their commonly cited example: "This, that, and the other loadstone, attracts iron, therefore all loadstones do?" Or why is not the former of these instances as good reasoning as the latter?
In the case of the balls, we cannot assign or imagine any reason why one should be white because others are so; any supposable connexion between the circumstance of the balls being together in the bag, and their colour. There is no tendency to fancy or expect it. On the other hand, in the case of the loadstone, having observed the effect, in a few instances, we feel a natural tendency to imagine that the same magnetic property subsists whenever we perceive the same external characteristics. We cannot avoid being persuaded that there is a connexion between that particular darkness of colour, weight, hardness, texture, &c., by which we recognise the mineral, and a magnetic power, though we may be at a loss to explain or assign the ground for it.
Yet the only thing which seems at all to warrant the induction from a limited number of instances, is the reasonableness of such an intuitive persuasion. When, therefore, we have only a limited number of instances, which we can examine (and such is the
case, in fact, in almost all physical inquiries,) no inductive inferences can properly be made, unless we feel assured of some probable ground for expecting a common connexion to subsist between the individual cases. Can we, then, succeed in tracing any probable principle to which the existence of such a persuasion may be traced?-Can we analyse it up to any rational ground of belief? This is a most important point of our inquiry; and to it our attention must next be directed. (See Note A.)
Belief in the Uniformity of Nature.
Now there is one grand, fundamental principle, without which no induction of laws from particular instances, no generalizations of individual truths, no regular or systematic study of nature, could ever proceed and this is our conviction of a permanence and uniformity in the order of natural things: our belief that, that which has happened in succession for days and years past, will, under the same circumstances, continue to happen for time to come: our persuasion that what so takes place in one instance, in one place, will and does take place, under the same conditions, in all other instances, and in all other places. We suppose, that is, that nature is so constituted, that there exists some principle of undeviating regularity in the connexion of qualities and properties, of causes and effects, even though we should fail in always tracing it.
This belief undoubtedly exists and operates in very different degrees in different minds. But a share of it, at least, is so universal, that some metaphysicians have been disposed to regard it as constituting one of the inherent principles of our nature*. Thus, the most ignorant person infers that the sun will rise to-morrow, and for succeeding days and years, because he has so regularly witnessed it before; and that a stone falls to the ground as constantly in America as in Europe.
In the limited form in which we commonly notice the operation of this sort of intuitive persuasion, it certainly does not amount to anything like a philosophical conviction of the uniformity of natural causes. It is, doubtless, restricted to certain isolated classes of facts, which in all their circumstances are constantly falling under the observation. In those limited instances, the individual, perhaps, relies on their recurrence from mere habit, which probably does not produce in his mind any general belief that other events beyond the limits of his observation are regulated by any like constant uniformity. Nor when the idea is suggested is he able to perceive the force of the inference from analogy; but, probably, imagines all things beyond the precise extent of his observation to be destitute of any determinate order, and the course of events in
* Reid and Turgot consider it an ultimate principle of the human mind. Reid calls it specifically "The inductive principle."-Inquiry into Human Mind, ch. vi. § 24.