[Footnote 3: I have said that there is little risk of confusion in using the word Opposition in its technical or limited sense. There is, however, a little. When it is said that these Inferences are based on Opposition, or that Opposition is a mode of Immediate Inference, there is confusion of ideas unless it is pointed out that when this is said, it is Opposition in the ordinary sense that is meant. The inferences are really based on the rules of Contrary and Contradictory Opposition; Contraries cannot both be true, and of Contradictories one or other must be.] CHAPTER III. THE IMPLICATION OF PROPOSITIONS.--IMMEDIATE FORMAL INFERENCE. --EDUCATION. The meaning of Inference generally is a subject of dispute, and to avoid entering upon debatable ground at this stage, instead of attempting to define Inference generally, I will confine myself to defining what is called Formal Inference, about which there is comparatively little difference of opinion. FORMAL INFERENCE then is the apprehension of what is implied in a certain datum or admission: the derivation of one proposition, called the CONCLUSION, from one or more given, admitted, or assumed propositions, called the PREMISS or PREMISSES. When the conclusion is drawn from one proposition, the inference is said to be IMMEDIATE; when more than one proposition is necessary to the conclusion, the inference is said to be MEDIATE. Given the proposition, "All poets are irritable," we can immediately infer that "Nobody that is not irritable is a poet"; and the one admission implies the other. But we cannot infer immediately that "all poets make bad husbands". Before we can do this we must have a second proposition conceded, that "All irritable persons make bad husbands". The inference in the second case is called Mediate.[1] The modes and conditions of valid Mediate Inference constitute Syllogism, which is in effect the reasoning together of separate admissions. With this we shall deal presently. Meantime of Immediate Inference. To state all the implications of a certain form of proposition, to make explicit all that it implies, is the same thing with showing what immediate inferences from it are legitimate. Formal inference, in short, is the eduction of all that a proposition implies. Most of the modes of Immediate Inference formulated by logicians are preliminary to the Syllogistic process, and have no other practical application. The most important of them technically is the process known as Conversion, but others have been judged worthy of attention. AEQUIPOLLENT OR EQUIVALENT FORMS--OBVERSION. AEquipollence or Equivalence ([Greek: Isodynamia]) is defined as the perfect agreement in sense of two propositions that differ somehow in expression.[2]