Charles S. Peirce
Chapter IV. Of Reality
MS 205 (Robin 371, 333): Writings 3, 60-61
Investigation supposes a true and a false, truth and falsity being independent of all opinion upon the matter. The name real is applied to that which is independent of how you or I or any number of minds think it to be.
It is a truism to say that the character of what I think depends entirely on what I think it to be. The real is not, therefore, per se an immediate object of thought, even though my thought may happen to coincide with it. Yet the real must influence thought or I could not by following any rules of reasoning arrive at any truth.
Investigation consists necessarily of two parts, one by which a belief is geiierated from other beliefs, which is called reasoning; and another by which new elements of belief are brought into the mind, which is called observation. Thus, the conclusions depend entirely upon the observations. But while the ultimate conclusion is one and the same in the minds of all who push investigation far enough, the observations on which it hangs are for every man private and peculiar. The observations which I made yesterday are not the same that I make today; nor are simultaneous observations from different situations or with other different circumstances the same. Two men cannot therefore make the same observation. We may go further and say that no two observations are in themselves in any degree alike. The judgment that they are alike is not contained in either observation (since they do not relate to one another) but is a belief generated by the two beliefs in which the two observations immediately result, so that it is an inference of reasoning, as that has just been defined. Thus our reasonings begin with the most various premises, which have not in themselves anything in common, but which so determine our beliefs as to lead us at last to one destined conclusion.
Here is the whole statement of facts from which we must infer whatever we can know of the mode of being of the real. But there is no additional fact which we can infer from these facts. For they embrace everything which takes place in thought, and as to anything out of thought we can know nothing.