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302 G. E. MOORE : tions, and that they approach to universality in the sense that many of them are prior to a very great number of other truths, will hardly he denied. And that they coincide to a remarkable degree with the class of ' necessary truths ' seems no less evident. But moreover they seem to coincide with the class of ' most certain ' propositions, in any sense of certainty which is not psychological. For any one who is looking for a perfectly certain proposition from which to de- duce his system of philosophy will in general try to show that it is logically prior to all other propositions. We may take as an instance the famous ' Cogito, ergo sum '. Here the conclusion that ' I am,' because I think, is made by way of logical priority : and it really is logically prior. How far Descartes used the same argument in defence of the pro- position that he thought, I am unaware : the certainty that he primarily claimed for it is certainly a psychological one, namely that he could not doubt it. But modern idealistic descendants of his constantly claim superior certainty for the ' Cogito ' itself, on the ground that it is logically prior to other propositions. Many will say straight out that thought is presupposed in all existence and all truth, and will draw the conclusion that the existence of thought is therefore the primary certainty. Others will say, in more popular forms : You cannot deny that, whatever you think, it is implied that you do think it ; and therefore the ultimate certainty is that you do think it, not that what you think is true : if you deny that you are making a statement, it is impossible to argue with you. Whether or not the statements which are thus argued to be more certain are really logically prior, is another question ; but it is worth while pointing out that those who use this argument are admitting the proposition that ' Logical priority is a test of certainty ' to be at least as certain as the proposition which they endeavour to establish by its means : this proposition is, at all events, logically prior to their argu- ment. And so, if we say that no proposition is necessary in itself, but that when we call it necessary we can only mean that it is connected in a certain way with other propositions, it may be asked : But what of this connexion ? Is not that necessary in itself? I should answer: Only in the same sense as those propositions, which it makes necessary, are necessary. For every statement of the form : This is in- volved in that, is itself a proposition ; and when we say : If you admit that, you must admit this : they are necessarily connected ; we only mean : This follows from that ; and the general principle that what follows from a truth is itself true