We also see why a valuable means for the discovery of truth is given by the inversion of platitudinous implications. It may happen that another platitude is the result of inversion; but it is the fate of any true remark, especially if it is easy to remember by reason of a paradoxical form, to become a platitude in course of time. There are rare cases of a platitude remaining unrepeated for so long that, by a converse process, it has become paradoxical. Such, for example, is Plato's remark that a lie is less important than an error in thought. Of late years, a method of disguising platitudes as paradoxes has been too extensively used by Mr. G. K. Chesterton. The method is as follows. Take any proposition _p_ which holds of an entity _a_; choose _p_ so that it seems plausible that _p_ also holds of at least two other entities _b_ and _c_; call _a_, _b_, _c_, and any others for which _p_ holds or seems to hold, the class A, and _p_ the "A-ness" or "A-ity" of A; let _d_ be an entity for which _p_ does not hold; and put _d_ among the A's when you think that nobody is looking. Then state your paradox: "Some A's do not have A-ness." By further manipulation you can get the proposition "No A's have A-ness." But it is possible to make a very successful _coup_ if A is the null-class, which has the advantage that manipulation is unnecessary. Thus, Mr. Chesterton, in his _Orthodoxy_ put A for the class of doubters who doubt the possibility of logic, and proved that such agnostics refuted themselves--a conclusion which seems to have pleased many clergymen. In this way, Mr. Chesterton has been enabled readily to write many books and to maintain, on almost every page, such theses as that simplicity is not simple, heterodoxy is not heterodox, poets are not poetical, and so on; thereby building up the gigantic platitude that Mr. Chesterton is Chestertonian. In the chapter on Identity we have illustrated the use of a case of the principle that any proposition implies any true proposition. This important principle may be called _the principle of the irrelevant premiss_;[53] and is of great service in oratory, because it does not matter what the premiss is, true or false. There is a _principle of the irrelevant conclusion_, but, except in law-courts, interruptions of meetings, and family life, this is seldom used, partly because of the limitation involved in the logical impossibility for the conclusion to be false if the premiss be true, but chiefly because the conclusion is more important than the premiss, being usually a matter of prejudice. Certain modern logicians, such as Frege, have found it necessary so to extend the meaning of implication of _q_ by _p_ that it holds when _p_ is not a proposition at all. Hitherto, politicians, finding that either identical or false propositions are sufficient for their needs, have made no use of this principle; but it is obvious that their stock of arguments would be vastly increased thereby.