Opposed to a truism is a Contradiction in Terms; that is, the denying of a subject something which it connotes (or which belongs to its definition), or the affirming of it something whose absence it connotes (or which is excluded by its definition).  A verbal proposition is necessarily true, because it is tautologous; a contradiction in terms is necessarily false, because it is inconsistent.  Yet, as a rhetorical artifice, or figure, it may be effective:  that ’the slave is not bound to obey his master’ may be a way of saying that there ought to be no slaves; that ‘property is theft,’ is an uncompromising assertion of the communistic ideal.  Similarly a truism may have rhetorical value:  that ’a Negro is a man’ has often been a timely reminder, or even that “a man’s a man.”  It is only when we fall into such contradiction or tautology by lapse of thought, by not fully understanding our own words, that it becomes absurd.

Real Propositions comprise the predication of Propria and Accidentia.  Accidentia, implying a sort of empirical law, can only be established by direct induction.  But propria are deduced from (or rather by means of) the definition with the help of real propositions, and this is what is called ‘arguing from a Definition.’  Thus, if increasing capacity for co-operation be a specific character of civilisation, ‘great wealth’ may be considered as a proprium of civilised as compared with barbarous nations.  For co-operation is made most effectual by the division of labour, and that this is the chief condition of producing wealth is a real proposition.  Such arguments from definitions concerning concrete facts and causation require verification by comparing the conclusion with the facts.  The verification of this example is easy, if we do not let ourselves be misled in estimating the wealth of barbarians by the ostentatious “pearl and gold” of kings and nobles, where 99 per cent. of the people live in penury and servitude.  The wealth of civilisation is not only great but diffused, and in its diffusion its greatness must be estimated.

To argue from a definition may be a process of several degrees of complexity.  The simplest case is the establishing of a proprium as the direct consequence of some connoted attribute, as in the above example.  If the definition has been correctly abstracted from the particulars, the particulars have the attributes summarised in the definition; and, therefore, they have whatever can be shown to follow from those attributes.  But it frequently happens that the argument rests partly on the qualities connoted by the class name and partly on many other facts.