only importance I can claim for the subject I shall investigate is that it seems to me to be a matter upon which not Idealists only, but all philosophers and psychologists also, have been in error, and from their erroneous view of which they have inferred (validly or invalidly) their most striking and interesting conclusions. And that it has even this importance I cannot hope to prove. If it has this importance, it will indeed follow that all the most striking results of philosophy—Sensationalism, Agnosticism and Idealism alike—have, for all that has hitherto been urged in their favour, no more foundation than the supposition that a chimera lives in the moon. It will follow that, unless new reasons never urged hitherto can be found, all the most important philosophic doctrines have as little claim to assent as the most superstitious beliefs of the lowest savages. Upon the question what we have reason to believe in the most interesting matters, I do, therefore, think that my results will have an important bearing; but I cannot too clearly insist that upon the question whether these beliefs are true they will have none whatever.
The trivial proposition which I propose to dispute is this: that esse is percipi. This is a very ambiguous proposition, but, in some sense or other, it has been very widely held. That it is, in some sense, essential to Idealism, I must for the present merely assume. What I propose to show is that, in all the senses ever given to it, it is false.
But, first of all, it may be useful to point out briefly in what relation I conceive it to stand to Idealistic arguments. That wherever you can truly predicate esse you can truly predicate percipi, in some sense or other, is, I take it, a necessary step in all arguments, properly to be called Idealistic, and, what is more, in all arguments hitherto offered for the Idealistic conclusion. If esse is percipi, this is at once equivalent to saying that whatever is is experienced; and this, again, is equivalent, in a sense, to saying that whatever is is something mental. But this is not the sense in which the Idealist conclusion must maintain that Reality is mental. The Idealist conclusion is that esse is percipere; and hence, whether esse be percipi or not, a further and different discussion is needed to show whether or not it is also percipere. And again, even if esse be percipere, we need a vast quantity of further argument to show that what has esse has also those higher mental qualities which are denoted by spiritual. This is why I said that the question I should discuss, namely, whether or not esse is percipi, must be utterly insufficient either to prove or to disprove that reality is spiritual. But, on the other hand,
