What Professor James says in this passage seems to me so indisputably true as fully to justify the vigour of his language. It is as clear as anything can be that it would not be useful for any man's mind to be _always_ occupied with the true idea that he had certain faults and blemishes; or to be _always_ occupied with the idea that twice two are four. It is clear, that is, that, if there are times at which a particular true idea is useful, there certainly are other times at which it would _not_ be useful, but positively in the way. This is plainly true of nearly all, if not quite all, our true ideas. It is plainly true with regard to nearly all of them that, even if the occasions on which their occurrence is useful are many, the occasions on which their occurrence would _not_ be useful are many more. With regard to most of them it is true that on most occasions they will, as Professor James says elsewhere, "be practically irrelevant, and had better remain latent."
It is, then, quite clear that almost any particular true idea _would_ not be useful at all times and that the times at which it would _not_ be useful, are many more than the times at which it would. And what we have to consider is whether, in just this sense in which it is so clear that most true ideas would _not_ be useful at most times, it is nevertheless true that all our true ideas _are_ useful. Is this so? Are all our true ideas useful?
Professor James, we see, has just told us that there are ever so many occasions upon which a particular true idea, such as that 2 + 2= 4, _would_ not be useful--when, on the contrary, it would be positively in the way. And this seems to be indisputably clear. But is not something else almost equally clear? Is it not almost equally clear that cases, such as he says _would_ not be useful, do sometimes actually happen? Is it not clear that we do actually sometimes have true ideas, at times when they are not useful, but are positively in the way? It seems to me to be perfectly clear that this does sometimes occur; and not sometimes only, but very commonly. The cases in which true ideas occur at times when they are useful, are, perhaps, far _more_ numerous; but, if we look at men in general, the cases in which true ideas occur, at times when they are not useful, do surely make up positively a very large number. Is it not the case that men do sometimes dwell on their faults and blemishes, when it is _not_ useful for them to do so? when they would much better be thinking of something else? Is it not the case that they are often unable to get their minds away from a true idea, when it is harmful for them to dwell on it? Still more commonly, does it not happen that they waste their time in acquiring pieces of information which are no use to them, though perhaps very useful to other people? All this seems to me to be undeniable--just as undeniable as what Professor James himself has said; and, if this is so, then, in one sense of the words, it is plainly not true that all, or nearly all, our true ideas are useful. _In one sense of the words._ For if I have the idea that 2+2=4 on one day, and then have it again the next, I may certainly, in a sense, call the idea I have on one day _one_ idea, and the idea I have on the next _another._ I have had two ideas that 2+2=4, and not one only. Or if two different persons both think that I have faults, there have been two ideas of this truth and not one only. And in asking whether _all_ our true ideas are useful, we might mean to ask whether _both_ of these ideas were useful and not merely whether one of them was. In this sense, then, it is plainly not true that _all_ our true ideas are useful. It is not true, that is, that every true idea is useful, _whenever it occurs._