ABSTRACT
This chapter is concerned with the conditions that are necessary in order that a deductive inference may be valid. It recognizes that the systematic investigation of the conditions of valid thinking forms a part of logic. The chapter distinguishes inference from other mental processes that may easily be confused with it. The chapter argues that a judgement is sometimes taken to be immediate, which later, can be seen to have involved the drawing of a conclusion from a datum. It defines inference more shortly by saying that inference is the mental process in which a thinker passes from one or more propositions to some other proposition connected with the former in a certain way. The chapter considers J. S. Mill's theory of the syllogism. The converse does not hold, since implication is a non-symmetrical relation.
