And plainly, in the first place, the mere fact that the same set of words, as in the instances I have given, really are true at one time and false at another, does not afford any presumption that anything which they stand for is true at one time and false at another. For the same words may obviously be used in different senses at different times; and hence though the same words, which formerly expressed a truth, may cease to express one, that may be because they now express a _different_ idea, and not because the idea which they formerly expressed has ceased to be true. And that, in instances such as I have given, the words _do_ change their meaning according to the time at which they are uttered or thought of, is I think, evident. If I use now the words "I am in this room," these words certainly express (among other things) the idea that my being in this room is contemporary with my present use of the words; and if I were to use the same words to-morrow, they would express the idea that my being in this room to-morrow, was contemporary with the use of them _then._ And since my use of them then would not be the same fact as my use of them now, they would certainly then express a different idea from that which they express now. And in general, whenever we use the present tense in its primary sense, it seems to me plain that we do mean something different by it each time we use it. We always mean (among other things) to express the idea that a given event is contemporary with our actual use of it; and since our actual use of it on one occasion is always a different fact from our actual use of it on another, we express by it a different idea each time we use it. And similarly with the past and future tenses. If anybody had said in 1807 "Napoleon is dead," he would certainly have meant by these words something different from what I mean by them when I use them now. He would have meant that Napoleon's death occurred at a time previous to _his_ use of those words; and this would not have been true. But in this fact there is nothing to show that if he _had_ meant by them what I mean now, his idea would not have been as true then as mine is now. And so, if I say "It will rain to-morrow," these words have a different meaning to-day from what they would have if I used them to-morrow. What we mean by "to-morrow" is obviously a different day, when we use the word on one day, from what we mean by it when we use it on another. But in this there is nothing to show that if the idea, which I _now_ mean by "It will rain to-morrow," _were_ to occur again to-morrow, it would not be true then, if it is true now. All this is surely very obvious. But, if we take account of it, and if we concentrate our attention not on the words but on what is meant by them, is it so certain that what we mean by them on any one occasion ever changes from true to false? If there were to occur to me to-morrow the very same idea which I now