existence of the earth cannot be denied ‘for when I speak of “philosophers” I mean, of course, as we all do, exclusively philosophers who have been human beings, with human bodies that have lived on the earth’.
The argument is not entirely convincing as it stands, since there is surely nothing to prevent the sceptic presenting his or her position in a more guarded way that avoids commitment to the supposed common-sense view (Descartes, indeed, aimed to do just that). Moore none the less succeeds in raising the interesting thought that the philosopher’s job might be not so much to propound high-flown theories as to remove the confusions and mistakes of previous theorists. The idea was taken up in a more sophisticated way by the famous Austrian philosopher Ludwig Wittgenstein, who argued in On Certainty (first published in 1969, eighteen years after his death) that the basic propositions instanced by Moore form part of a fundamental framework that is unavoidable if it is even to make sense to raise questions about what we know: ‘I did not get my picture of the world by satisfying myself of its correctness. No: it is the inherited background against which I distinguish between true and false … All testing, all confirmation and disconfirmation of a hypothesis, takes place within a system. And this system is not a more or less arbitrary and doubtful point of departure for all our arguments; no, it belongs to the essence of what we call an argument. The system is not so much the point of departure as the element within which arguments have their life … I should like to say Moore does not know what he asserts he knows, but it stands fast for him, as also for me; regarding it as absolutely solid is part of our method of doubt and enquiry.’1 Whatever judgement one passes on Moore’s approach, it continues to provoke important questions about the relationship between philosophical theorizing about knowledge and the seemingly unshakeable everyday beliefs which we all share.
In what follows I have merely tried to state, one by one, some of the most important points in which my philosophical position differs from positions which have been taken up by some other philosophers … I am going to begin by enunciating, under the heading (1), a whole long list of propositions, which may seem, at first sight, such obvious truisms as not to be worth stating: they are, in fact, a set of propositions, every one of which (in my own opinion) I know, with certainty, to be true …
(1) The propositions to be included in this list are the following. There exists at present a living human body, which is my body. This body was born at a certain time in the past, and has existed continuously ever since, though not without undergoing changes; it was, for instance, much smaller when it was born, and for some time afterwards, than it is now. Ever since it was born, it has been either in contact with or not far from the surface of the earth; and, at every moment since it was born, there have also existed many other things, having shape and size in three dimensions (in the same familiar sense in which it has), from which it has been at various distances (in the familiar sense in which it is now at a distance both from that mantelpiece and from that bookcase, and at a greater distance from the bookcase than it is from the mantelpiece); also there have (very often, at all events) existed some other things of this kind with which it was in contact (in the familiar sense in which it is now in contact with the pen I am holding in my right hand and with some of the clothes I am wearing). Among the things which have, in this sense, formed part of its environment (i.e., have been either in contact with it, or at some distance from it, however great) there have, at every moment since its birth, been large numbers of other living human bodies, each of which has like it, (a) at some time been born, (b) continued to exist from some time after birth, (c) been, at every moment of its life after birth, either in contact with or not far from the surface of the earth; and many of these bodies have already died and ceased to exist. But the earth had existed also for many years before my body was born; and for many of these years, also, large numbers of human bodies had, at every moment, been alive upon it; and many of these bodies had died and ceased to exist before it was born. Finally (to come to a different class of propositions), I am a human being, and I have, at different times since my body was born, had many different experiences, of each of many different kinds: e.g., I have often perceived both my own body and other things which formed part of its environment, including other human bodies; I have not only perceived things of this kind, but have also observed facts about them, such as, for instance, the fact, which I am now observing, that that mantelpiece is at present nearer to my body than that bookcase; I have been aware of other facts, which I was not at the time observing, such as, for instance, the fact, of which I am now aware, that my body existed yesterday and was then also for some time nearer to that mantelpiece than to that bookcase; I have had expectations with regard to the future, and many beliefs of other kinds, both true and false; I have thought of imaginary things and persons and incidents, in the reality of which I did not believe; I have had dreams; and I have had feelings of many different kinds. And, just as my body has been the body of a human being, namely myself, who has, during his lifetime, had many experiences of each of these (and other) different kinds; so, in the case of very many of the other human bodies which have lived upon the earth, each has been the body of a different human being, who has, during the lifetime of that body, had many different experiences of each of these (and other) different kinds.
(2) I now come to [a] single truism which, as will be seen, could not be stated except by reference to the whole list of truisms, just given in (1). This truism also (in my own opinion) I know, with certainty, to be true; and it is as follows: … Each of us (meaning by ‘us’, very many human beings of the class defined) has frequently known, with regard to himself or his body and the time at which he knew it, everything which, in writing down my list of propositions in (1), I was claiming to know about myself or my body and the time at which I wrote that proposition down … Just as I knew (when I wrote it down) ‘There exists at present a living human body which is my body’, so each of us has frequently known with regard to himself at some other time the different but corresponding proposition, which he could then have properly expressed by, ‘There exists at present a human body which is my body’; … and so on, in the case of each of the propositions enumerated in (1) …
In what I have just said, I have assumed that there is some meaning which is the ordinary or popular meaning of such expressions as ‘The earth has existed for many years past’. And this, I am afraid, is an assumption which some philosophers are capable of disputing. They seem to think that the question ‘Do you believe that the earth has existed for many years past?’ is not a plain question, such as should be met either by a plain ‘Yes’ or ‘No’, or by a plain ‘I can’t make up my mind’, but is the sort of question which can be properly met by: ‘It all depends on what you mean by ‘“the earth”’ and ‘“exists”’ and ‘“years”’… It seems to me that such a view is as profoundly mistaken as any view can be. Such an expression as ‘The earth has existed for many years past’ is the very type of an unambiguous expression, the meaning of which we all understand. Anyone who takes a contrary view must, I suppose, be confusing the question whether we understand its meaning (which we all certainly do) with the entirely different question whether we know what it means, in the sense that we are able to give a correct analysis of its meaning. The question what is the correct analysis of the proposition meant on any occasion … by ‘The earth has existed for many years past’ is, it seems to me, a profoundly difficult question, and one to which, as I shall presently urge, no one knows the answer. But to hold that we do not know what, in certain respects, is the analysis of what we understand by such an expression, is an entirely different thing from holding that we do not understand the expression. It is obvious that we cannot even raise the question how what we do understand by it is to be analysed, unless we do understand it. So soon, therefore, as we know that a person who uses such an expression is using it in its ordinary sense, we understand his meaning. So that in explaining that I was using the expressions used in (1) in their ordinary sense (those of them which have an ordinary sense, which is not the case with quite all of them), I have done all that is required to make my meaning clear.
But now, assuming that the expressions which I have used to express
