Stevenson ([1938]) introduced the concept of persuasive definition in the following terms:

In any “persuasive definition” the term defined is a familiar one, whose meaning is both descriptive and strongly emotive. The purport of the definition is to alter the descriptive meaning of the term, usually by giving it greater precision within the boundaries of its customary vagueness; but the definition does not make any substantial change in the term’s emotive meaning. And the definition is used, consciously or unconsciously, in an effort to secure, by this interplay between emotive and descriptive meaning, a redirection of people’s attitudes. (Stevenson [1938], p. 210-211)

To make a definition persuasive, within Stevenson’s meaning, its descriptive content must be redefined, whilst its “emotional force” must be kept intact so as to be applied to the redefined content. Stevenson gives the following example; A and B are “discussing a mutual friend” (id, p. 211.)

— A points out a number of shortcomings of that person (education, conversation, literary references, subtlety of spirit) and concludes that “he is definitely lacking in culture.”

— B describes this friend under a number of favorable lines (imagination, sensibility, originality) and concludes that “he is a man of far deeper culture than many of us who have had superior advantages in education”.

First, both A and B value culture, and are willing to give the word culture and the judgment “X is a cultured person” a positive emotional orientation. Moreover, the word culture has a vague descriptive sense; B carves out of this descriptive sense a new definition, and shows that it fits their mutual friend. Stevenson analyses B‘s argumentative move as follows

His purpose was to redirect A‘s attitudes, feeling that A was insufficiently appreciative of their friend’s merits (id., p. 211).

The argumentative trick is located at point (b), that is:

(a) B wishes to value his friend.
(b) He redefines culture “within the boundaries of its customary vagueness” according to qualities possessed by his friend;
(c) and he concludes that his friend is cultured;
(d) and the friend benefits from the positive opinion associated with the idea of culture and cultured person.

Thus, a persuasive definition redefines the descriptive contents of a term not on the basis of context-free, objective general considerations, but with a view to applying this term to a pre-determined person, a singular case. This is what would make it deceptive. It should be noted however that Stevenson attributes a persuasive definition to B only. Yet it might be argued that A also carves his definition out of the vague meaning of “culture”, “within the boundaries of its customary vagueness”. A thus has a persuasive definition, in much the same way as B, of “culture” as literary references, etc., allowing him to exclude the common friend from the circle of the cultivated. A seeks to influence B just as much as B tries to influence A.

Point (d) implies that the argumentative orientation (called here “the emotive content”) is independent of the cognitive content, and not affected by the redefinition. Thus, this orientation has to be attached directly to the signifier.

As it operates a redistribution of meaning, persuasive definition exploits the processes of distinguo and dissociation.

A persuasive definition is a definition that does not meet the condition of separability between, on the one hand, the construction process of the definition, and, on the other hand, the use of the definitional features to include an individual or a special case in the category it determines and calls it by the category’s name. In other words, a persuasive definition is a definition which is conditioned by the intention of including a specific object, that is, an ad hoc definition, imagined or altered on the spot, for the purpose at hand, S. Orientation.

The criteria of what is “good school task” must be applied regardless of the categorization of such work in or out of that category. A skewed definition does not meet this criterion:

A good school task is a task in which student get involved and on which they worked hard. My son spent his weekend on his history course. Thus he handed in an excellent piece of work, and deserves a good grade.

The category “is a good school task” has been redefined so that it can apply to Mr. Doe’s son, leaving aside the contents of the work, traditionally regarded as the decisive factor. The target has been re-designed to fit the arrow, and the limited capacities of the archer.