Sigmund Freud used the term purposive idea, above all in his early psychoanalytic writings, to refer to the orienting role of an idea when it is conducive to the sudden appearance of a train of thought (ideas, affects, representations, fantasies, and so on). The stages in this train of thought converge in the direction of this idea, which thus itself seems to be the goal of all of this psychic work.
Freud's main discussion of this notion is found in The Interpretation of Dreams (1900a; chapter 7, section 1); thereafter he returned to it only sporadically. His aim in this passage was to refute an objection that had been raised against his method of dream analysis by means of free association; his critics contended the material produced in this way could consist only of isolated fragments and could have no overall meaning. This objection came out of an understanding of associationism in which, at the time, ideas that thus appeared "by chance" could only be brought together based on formal criteria (synonymy, assonance, and so on) or chance (temporal coincidence, for example). It is remarkable that Freud, who elsewhere made extensive use of these formal or contingent factors in association, in this passage challenged the idea of a train of thought occurring by chance. He pointed out that conscious thought is always directed toward a goal to be reached (solution of a problem, preparing for an action, and so on). The same is true, he said, when a train of thought is unconscious and/or bears upon representations that are themselves unconscious: It is always directed toward a goal, even if the subject is unaware of it. Thereafter, when someone was asked, after relating a dream, to proceed by free association, the sequence of the dreamer's evocations followed an orientation homologous to the one that presided over the dream-work, a process in which the goal to be reached was the fulfillment of a wish. The same applied in the analysis of a symptom, homologous to the work of producing this symptom, which could thus be decrypted.
Thus, although Freud subsequently returned to this term only intermittently in his later works, he based the notion on two essential principles: First, the elements of thought, notably representations, are linked together in an ordered sequence (the analysis of several such trains of thought leading in general to a "nodal point" at the heart of the subject's problematics); and, second, this sequence is ordered by a finality.
See also: Fundamental rule; Interpretation of Dreams, The .
Freud, Sigmund (1900a). The interpretation of dreams. Part I., SE, 4: 1-338; Part II, SE, 5: 339-625.