service to philosophy has consisted in giving a name to and erecting into a principle, a type of fallacy to which experience had shown philosophers, along with the rest of mankind, to be addicted. No wonder that he has followers and admirers. I have shown then, so far, that when the Idealist asserts the important principle 'Esse is _percipi'_ he must, if it is to be true, mean by this that: Whatever is experienced also _must_ be experienced. And I have also shown that he _may_ identify with, or give as a reason for, this proposition, one which must be false, because it is self contradictory. But at this point I propose to make a complete break in my argument. '_Esse_ is _percipi_,' we have seen, asserts of two terms, as distinct from one another as 'green' and 'sweet,' that whatever has the one has also the other: it asserts that 'being' and 'being experienced' are necessarily connected: that whatever _is_ is _also_ experienced. And this, I admit, cannot be directly refuted. But I believe it to be false; and I have asserted that anybody who saw that '_esse_ and _percipi_' _were_ as distinct as 'green' and 'sweet' would be no more ready to believe that whatever _is_ is _also_ experienced, than to believe that whatever is green is also sweet. I have asserted that no one would believe that '_esse_ is _percipi_' if they saw how different _esse_ is from _percipi:_ but _this_ I shall not try to prove. I have asserted that all who do believe that '_esse_ is _percipi_' identify with it or take as a reason for it a self-contradictory proposition: but this I shall not try to prove. I shall only try to show that certain propositions which I assert to be believed, are false. That they are believed, and that without this belief '_esse_ is _percipi'_ would not be believed either, I must leave without a proof. I pass, then, from the uninteresting question 'Is _'esse percipi?'_ to the still more uninteresting and apparently irrelevant question 'What is a sensation or idea?' We all know that the sensation of blue differs from that of green. But it is plain that if both are _sensations_ they also have some point in common. What is it that they have in common? And how is this common element related to the points in which they differ? I will call the common element 'consciousness' without yet attempting to say what the thing I so call _is._ We have then in every sensation two distinct terms, (1) 'consciousness,' in respect of which all sensations are alike; and (2) something else, in respect of which one sensation differs from another. It will be convenient if I may be allowed to call this second term the 'object' of a sensation: this also without yet attempting to say what I mean by the word.