…logical criticism cannot go behind perceptual facts, which are the first judgments which we make concerning percepts. A perceptual fact is therefore an abstract affair. Each such fact covers only certain features of the percept. I look at an object and think that it seems white. That is my judgment of the object perceived, or my judgment concerning the percept, but not the percept itself; and it is idle to attempt to criticize by any logic that part of the performance of the intellect which draws that judgment from the percept, for the excellent reason that it is involuntary and cannot be prevented or corrected. Such a fact which represents the percept in a very meagre way, although it is, in itself, a relatively isolated fact, – as isolated as any fact can be, – nevertheless does not, in itself, call for any explanation.
The real thinking-process presumably begins at the very percepts. But a percept cannot be represented in words, and consequently, the first part of the thinking cannot be represented by any logical form of argument. Our logical account of the matter has to start from a perceptual fact, or proposition resulting from thought about a percept – thinking in its own movement presumably of the same nature as that which we represent by arguments and inferences, but not so representable in consequence of a defect in that method of representation.
It is essential, at the very threshold of logic, to distinguish between a percept, which is what the senses perceive, and which is an object of study for the intellect, and a perceptual fact, which the understanding perceives in the percept, and which is the first fruit of observation. Photographs, even when they show no more than the eye can see, are most valuable in sciences of observation; they are stored up percepts. But they in no degree enable us to dispose with scientific descriptions, which are records of perceptual facts, the basis of all else in science.
In place of the percept, which, although not the first impression of sense, is a construction with which my will has had nothing to do, and may, therefore, properly be called the “evidence of my senses,” the only thing I carry away with me is the perceptual facts, or the intellect’s description of the evidence of the senses, made by my endeavor. These perceptual facts are wholly unlike the percept, at best; and they may be downright untrue to the percept. But I have no means whatever of criticizing, correcting or recomparing them, except that I can collect new perceptual facts relating to new percepts, and on that basis may infer that there must have been some error in the former reports, or on the other hand I may in this way persuade myself that the former reports were true. The perceptual facts are a very imperfect report of the percepts; but I cannot go behind that record. As for going back to the first impressions of sense, as some logicians recommend me to do, that would be the most chimerical of undertakings.
The data from which inference sets out and upon which all reasoning depends are the perceptual facts, which are the intellect’s fallible record of the percepts, or “evidence of the senses.” It is these percepts alone upon which we can absolutely rely, and that not as representative of any underlying reality other than themselves.