“Prevision” thus becomes the essential characteristic of scientific knowledge, and that independently of any utilitarian mental reservation. For the eventual applications of science do not determine its theoretical advance. The prevision with which we are here concerned consists solely in the possibility of knowing with certainty without observing. It is knowledge a priori in the Aristotelian sense of the word, of which mathematics present the most perfect model. A rectilinear triangle being given, I do not need experience to know with certainty that the sum of the angles in it is equal to two right angles. Thus understood prevision applies to the present, and even to the past, as well as to the future. When Comte writes “All science has prevision for its aim,”[38] we must understand: “All science tends to substitute deduction to experience, rational to empirical knowledge.” This prevision, a necessary consequence of the constant relations discovered between phenomena, will allow men never to mistake real science for fruitless erudition, which accumulates facts without deducing them one from another.
Thus the formula cited above enlarges itself: “Science is composed of laws and not of facts.” The more deduction is substituted to experience, the better is the extension and connection of our knowledge realised. Consequently, the more also does science draw near to that unity which is imperatively claimed by our understanding, and which is for it the criterion of truth. “Real science,” says Comte, “regarded from the highest point of view, has no other general object but to establish or to fortify unceasingly the intellectual order, which is the basis of all other order.”[39] The mind which applies itself to the contemplation of the world requires, before everything, to find it intelligible. “Real” science satisfies it, not in imagining wills and causes, as did theology and metaphysics, but in discovering order in the constant relations between phenomena. When this order is harmonious, that is to say, when the several classes of phenomena are conceived as homogenous, and as similarly governed by laws, “the spontaneous unity of our understanding is consolidated.” It matters little that the various orders of phenomena are given to us as irreducible to one another. The highest object of science is to determine the point of view from which all phenomena appear intelligible, and this point of view is one as the understanding itself is one.
III.
Perhaps it would have been easy to pass from this conception of positive science to a theory of knowledge, and to a metaphysical view of nature, both idealistic. But Comte neither could nor would push his theory in this direction. In this respect nothing is more significant than his way of understanding the relativity of science.
This relativity is usually presented as the conclusion of a criticism of our understanding, of its nature, of its bearings, and of its relations to its objects. But, according to Comte, an inquiry pursued on these lines, has no chance of reaching a conclusion. The only theory of knowledge which is positive and “real,” is drawn from the history of the human mind. The laws of the mind are only revealed in the examination of the successive products of its activity, that is to say in its beliefs and in its science. The relativity of science can therefore only be stated at first, as a fact, leaving it for subsequent inquiry to determine the reason of that fact. The law of the three States suffices for this, for it shows that man began by seeking for absolute knowledge. The philosophy to which he first turns is, at the same time, the most naïve and the most ambitious. But a necessary evolution causes him to abandon the pursuit of the absolute, first in its theological form and then in the metaphysical form. Having reached the positive state, man knows that his science, necessarily relative, is limited to “the systematic co-ordination of phenomena,” and the knowledge of their laws.
The condemnation which thus strikes researches bearing on the absolute is itself, moreover, only relative in character. It prejudges nothing respecting the ultimate solution of questions. Positive philosophy in no way takes sides in respect to these problems. It simply states that science has more and more cut them off from the number of those which it studies. Indeed it is impossible to apply the positive method to questions which concern the absolute. Now, this method being the only one which our mind can henceforth follow, at least if it wishes to maintain the logical unity which is its supreme requirement, it follows that these problems are in fact abandoned. Nothing more and nothing less. “Sound philosophy,” says Comte, “sets aside, it is true, insoluble questions”; but “in stating the motive of their rejection, it avoids denying anything respecting them, which would be contradictory to that systematic disuse by which alone uncontrovertible opinions must die out.” (Comte means: opinions which do not come within the range of positive discussion.) The problems relating to the essence of the soul or to the “substantia prima” will melt away, as the majority of the metaphysical problems which the scholastics put to themselves have already disappeared.
Even to positive science, we must be careful not to attribute an absolute character—that is to say, in a sense slightly different from the preceding one, but very frequently with Comte—a definite and immutable character. The laws which we can determine are never true except under certain conditions. We have no right to consider them as true absolutely. Newton’s law is demonstrated for our solar system: but do we know that it is verified in all the systems throughout space? Do not let us confound the world, which we can study with the united resources of observation and calculation with the universe, of which we know scarcely anything, and which outranges all our powers. In spite of the famous principle of the sufficient reason the absence of motives for negation does not constitute the right of affirmation, without any direct proof. Absolute notions, says Comte, seem to me so impossible that I would not even dare, whatever probability I may see in it, to warrant the necessary and unalterable perpetuity of the theory of gravitation restricted to the interior of our world, if one day, (which is moreover very difficult to admit) the precision of our present observations came to be perfected as much as we have done in comparison to Hipparchus.[40]
In the same way, must not attraction have seemed to be an absolute quality (that is to say an immutable one) of bodies, since neither change of shape, nor the passage from one physical constitution to another, nor any chemical metamorphosis, nor even the difference between the state of life and death could modify this quality, so long as the integrity of the substance was maintained? The Newtonian conception came and destroyed entirely at a signal stroke this character which must have appeared so indestructible, by showing that the weight of a body is a phenomenon purely relative to the position of this body in the world, or, more precisely, to its distance from the centre of the earth.[41]
In order that our positive science of any part of nature should be absolute, that is to say, final, it would have to be complete. But, as all things are caused or causing, helped or helping, according to Pascal’s expression, all the phenomena in a reciprocal universal action, all the laws relative one to another, our science will never be complete on any point. It only furnishes more or less imperfect approximations.[42] The discovery of new facts and new laws is always possible.
How many times does not positive science find itself obliged to modify and to readjust a system of long acquired notions, in order to make a place for new elements? This is a work often very laborious, but from which science never dreams of shrinking, knowing that it is made liable to it, so to speak, by definition, that is to say, that it is relative. Examples of this abound, not only in the history of physical and natural science, but even in that of so-called exact sciences. Do we not hear M. Poincaré declaring in accordance with Hertz, that given the system of Galileo and of Newton in mechanics it is impossible to give a satisfactory idea of mass and of force?[43]