And so the argument derived from marks of design in Nature may be stated in one or other of two ways:—it may be stated analogically or inductively. The difference between analogy and induction, which is not always duly considered, should be carefully marked. Analogy proceeds on partial, induction on perfect resemblance. The former marks a resemblance or agreement in some respects between things which differ in other respects: the latter requires a strict and entire similarity in those respects on which the inductive inference depends. The one by itself may only yield a probable conjecture, but the other, when combined with it, may produce a certain conviction. Accordingly the design argument may be thrown either into the analogical or the inductive form. Stated analogically, it stands thus: "There is an ascertained partial resemblance between organs seen in art and organs seen in nature; as, for instance, between the telescope and the eye.
"It is probable from analogy that there is in some further respect a partial resemblance between organs seen in art and organs seen in nature: in art the telescope has been produced by a contriver, analogy makes it probable that in nature the eye also will have been produced by a contriver."
But stated inductively, it stands thus: "If there be in nature the manifestation of supernatural contrivance, there must exist a supernatural contriver.
"There is in nature the manifestation of supernatural contrivance.
"Therefore a supernatural contriver,—God,—must exist."[284]
Combine the perfection of analogy with the principle of causality, and you have not only the verisimilitude or likelihood which prepares the way for belief, but also a positive proof resting on a fundamental law of reason. The inference of intelligence from marks of design in nature is not one of analogy, but of strict and proper induction; and accordingly we must either deny that there are marks of design in nature, thereby discarding the analogy, or do violence to our own reason by resisting the fundamental law of causality, thereby discarding the inductive inference. And of these two unavoidable alternatives, Mr. Holyoake seems to prefer the former: he will venture to deny the existence of design in nature, rather than admit the existence of design and resist the inevitable inference of a designing cause; for he is compelled in the long run to come round to this desperate confession, "What I supposed to be design in the opening of my argument is no longer design. My reverend friend is wrong in supposing that I admit design, and yet refuse to admit the force of the design argument."
But if he mistakes the general nature and conditions of the argument when he speaks of it as if it were a mere argument from analogy, his extension of the analogy, and the reasonings founded on it, are equally unjustifiable and inconclusive. He forgets that analogy proceeds on a partial resemblance in some respects, between things which differ in other respects, and that even induction itself requires a perfect resemblance only in those respects on which the inference depends. There may be such a resemblance between the marks of design in nature and in art as to warrant the inference of a contriver in both; and yet in other respects there may be a dissimilarity which cannot in the least affect the validity or the certainty of that inference. It is only when we extend the analogy beyond the inductive point, that the conclusion becomes, in some cases, merely probable, in others altogether doubtful. If we advance a step further than we are warranted to go by obvious and certain analogies, our conclusions must be purely conjectural, and cannot be accepted as inductive inferences. From what we know of this world, and of God's design in it to make Himself known to His intelligent creatures, we may infer, with some measure of probability, that other worlds may also be inhabited by beings capable, like ourselves, of admiring His works, and adoring His infinite perfections; but if we go further, and infer either that all these worlds must now be inhabited, or that the inhabitants must be in all respects constituted as we are, we pass far beyond the point to which our knowledge extends, and enter on the region of mere conjecture. And so when Mr. Holyoake extends the analogy, so as to include not only the marks of design, on which the inductive inference rests, but also the forms of organization, with which in the case of man, intelligence is at presented associated, although not identified, he goes beyond the point at which analogy and induction combine to give a certain conclusion, and introduces a conjectural element, which may well render his own inferences extremely doubtful, but which can have no effect in weakening the grounds of our confidence in the fundamental law, which demands an adequate cause for the marks of design in nature.
Mr. Ferrier has shown that "the senses are only contingent conditions of knowledge; in other words, it is possible that intelligences different from the human (supposing that there are such) should apprehend things under other laws, or in other ways, than those of seeing, hearing, touching, tasting, and smelling; or more shortly, our senses are not laws of cognition or modes of apprehension which are binding on intelligence necessarily and universally."—"A contingent law of knowledge" is defined as "one which, although complied with in certain cases in the attainment of knowledge, is not enforced by reason as a condition which must be complied with wherever knowledge is to take place. Knowledge is thus possible under other conditions than the contingent laws to which certain intelligences may be subject; in other words, there is no contradiction in affirming that an intelligent being may have knowledge of some kind or other without having such senses as we have."[285]
The application of analogy as a principle of judgment is subject to certain well-known limitations, which cannot be disregarded without serious risk of error. They are well stated by Dr. Hampden: "There are two requisites in order to every analogical argument:—1. That the two, or several particulars concerned in the argument should be known to agree in some one point; for otherwise they could not be referable to any one class, and there would consequently be no basis to the subsequent inference drawn in the conclusion. 2. That the conclusion must be modified by a reference to the circumstances of the particular to which we argue. For herein consists the essential distinction between an analogical and an inductive argument. Since, in an inductive argument, we draw a general conclusion, we have no concern with the circumstantial peculiarity of individual instances, but simply with their abstract agreement. Whereas, on the contrary, in an analogical argument, we draw a particular conclusion, we must enter into a consideration of the circumstantial peculiarity of the individual instance, in order to exhibit the conclusion in that particular form which we would infer. Whence it follows, that whilst by induction we obtain absolute conclusions, by analogy we can only arrive at relative conclusions, or such as depend for their absolute and entire validity on the coincidence of all the circumstances of the particular inferred with those of the particular from which the inference is drawn." Again: "The circumstances to which we reason may be considered of threefold character. They are either known or unknown. If they are known, they are either (1.) Such as we have no reason to think different, in any respect from those under which our observations have been made; or (2.) Such as differ in certain known respects from these last. (3.) They are unknown, where we reason concerning truths of which, from the state of our present knowledge, from the nature of our faculties, or from the accident of our situation as sojourners upon earth, we are totally ignorant."[286]
With these necessary limitations, suggested by the different circumstances in which analogy is applied, we shall have little difficulty in disposing of Mr. Holyoake's extension of Dr. Paley's argument. Not content with resemblance in some respects, he requires a sameness in all. He would exclude all dissimilarity, forgetting that analogy denotes a certain relation between two or more things which in other respects may be entirely different. We may see a resemblance between the marks of design in nature and the ordinary effects of design in art; and that perception of design gives rise to an intuitive conviction or inductive inference of a designing cause: thus far we proceed under the guidance of analogy, but on the sure ground of induction. If we go beyond this, and insist that the designing cause must be in all respects like ourselves, that if we be organized, He must be organized, that if we act by material organs He must act by the same, we exceed the limits of legitimate reasoning, and enter on the region of pure conjecture. But such conjectures, groundless as they are, and revolting as every one must feel them to be, can have no effect in shaking our confidence in the valid induction by which we infer from marks of design in nature the existence of a designing Cause.