Blackwoods Edinburgh Magazine | Page 9

not flow from, but regulate, our experience. A mechanical pressure, not accompanied by an equal and opposite pressure, can no more be given by experience than two unequal right angles. With the supposition of such inequalities, space ceases to be space, form ceases to be form, matter ceases to be matter." And again he says, "That the parallelogram of forces is a necessary truth;" a law of motion of which we surely can conceive its opposite to be true. In some of these instances Mr Whewell appears, by a confusion of thought, to have given to the physical fact the character of necessity which resides in the mathematical formula employed for its expression. Whether a moving body would communicate motion to another body--whether it would lose its own motion by so doing--or what would be the result if a body were struck by two other bodies moving in different directions--are questions which, if they could be asked us prior to experience, we could give no answer whatever to--which we can easily conceive to admit of a quite different answer to that which experience has taught us to give.
This distinction, which assigns a different mental origin to truths, simply because (from the nature of the subject-matter, as it seems to us) there is a difference with regard to the sort of certainty we feel of them, has always appeared to us most unphilosophical. It is admitted that we arrive at a general proposition through experience; there is no room, therefore, for quibbling as to the meaning of the term experience--it is understood that when we speak of a truth being derived from experience, we imply the usual exercise of our mental faculties; it is the step from a general to a universal proposition which alone occasions this perplexing distinction. The dogma is this--that experience can only teach us by a limited number of examples, and therefore can never establish a universal proposition. But if all experience is in favour of a proposition--if no experience has occurred even to enable the imagination to conceive its opposite, what more can be required to convert the general into a universal proposition?
Strange to say, the attribution of these characteristics of universality and necessity, becomes, amongst those who loudly insist upon the palpable nature of the distinction we are now examining, a matter of controversy; and there are a class of scientific truths, of which it is debated whether they are contingent or necessary. The only test that they belong to the latter order is, the impossibility of conceiving their opposites to be the truth; and it seems that men find a great difference in their powers of conception, and that what is impossible with one is possible with another. But (wisely, too) passing this over, and admitting that there is a distinction (though a very ill-defined one) between the several truths we entertain of this nature; namely, that some we find it impossible, even in imagination, to contradict, whilst of others we can suppose it possible that they should cease to be truths--does it follow that different faculties of the mind are engaged in the acquisition of them? Does nothing depend on the nature of the subject itself? "That two sides of a triangle," says Mr Whewell, "are greater than the third, is a universal and necessary geometrical truth; it is true of all triangles; it is true in such a way that the contrary cannot be conceived. Experience could not prove such a proposition." Experience is allowed to prove it of this or that triangle, but not as an inseparable property of a triangle. We are at a loss to perceive why the same faculties of the mind that can judge, say of the properties of animal life, of organized beings, cannot judge of the properties of a figure--properties which must immediately be conceived to exist the moment the figure is presented to the imagination. We say, for instance, of any animal, not because it is this or that animal, a sheep or an ox, but simply as animal, that it must sustain itself by food, by the process of assimilation. This, however, is merely a contingent truth, because it is in our power to conceive of organized beings whose substance shall not wear away, and consequently shall not need perpetual restoration. But what faculty of the mind is unemployed here that is engaged in perceiving the property of a triangle, that as triangle, it must have two sides greater than the third? The truths elicited in the two cases have a difference, inasmuch as a triangle differs from an animal in this, that it is impossible to conceive other triangles than those to which your truth is applicable, and therefore the proposition relating to the triangle is called a necessary truth. But surely