But, when it is said that observation gives us a reason for generalisations, two things may be meant neither of which I mean. In the first place, we popularly use "observation" in a sense in which we can be said to _observe_ the perceptions, feelings and thoughts of other people: in which, therefore, we can be said to observe the very things with regard to which I am asking what reason we have for believing in their existence. But it is universally[1] agreed that there is a sense in which no man can observe the perceptions, feelings or thoughts of any other man. And it is to this strict sense that I propose to confine the word. I shall use it in a sense, in which we can certainly be said to observe nothing but ourselves, our own perceptions, thoughts and feelings, and what we directly perceive. And in the second place, it may be said that observations made by another person may give _me_ a reason for believing some generalisation. And it is certainly the case that for many of the generalisations in which we all believe, if we have a reason in observation at all, it is not in _our own_ observation that we have it: part of our reason, at all events, lies in things which _other_ people have observed but which we ourselves have not observed. But in asking this particular question, I am not asking for reasons of this sort. The very question that I am asking is: What reason has any one of us for supposing that any other person whatever has ever made any observations? And just as, in the first meaning which I gave to this question, it meant: What thing, that any single man observes is such that it would probably not have existed, unless some other man had made a particular observation? So now I am asking: Which among the things, which _one single man observes_, are such that they would probably not have existed, unless it were true that some of them generally stood in certain relations to observations of some other person? I am asking: Which among _my own_ observations give me a reason for supposing that some of them are of a kind which are generally preceded or accompanied by observations of other people? Which, for instance, among my own observations give a good reason for the generalisation that when I hear certain words, somebody else has generally had certain particular thoughts, or that whenever anyone hears certain words, somebody else has generally had the thoughts which constitute what we call the meaning of those words? I am asking: Which among the vast series of observations, which any one individual makes during his lifetime, give a good reason for any generalisation _whatever_ of this kind--a generalisation which asserts that some of them are generally preceded by certain thoughts, perceptions or feelings in other persons? I quite admit that there are some generalisations of this kind for which the observations of _some_ particular men will _not_ give a reason. All that I ask is: