From wikipedia [ed.]: In Philosophie des Als Ob, [Vaihinger] argue[s] that human beings can never really know the underlying reality of the world, and that as a result we construct systems of thought and then assume that these match reality: we behave "as if" the world matches our models. In the preface to the English edition of his work, Vaihinger expresses his principle of Fictionalism: "an idea whose theoretical untruth or incorrectness, and therewith its falsity, is admitted, is not for that reason practically valueless and useless; for such an idea, in spite of its theoretical nullity, may have great practical importance."
Vaihinger's summary of the Philosophy of "As If" in the autobiographical chapter that begins the English edition (xlv-xlvii):
- A dichotomy exists between science, which concerns itself with matter in motion, and philosophy, which concerns itself with sensations (this antinomy cannot be mediated by reason, only through intuition and experience).
- The "striving" or struggle for existence that exists in all matter has evolved into will (the will to live and to dominate others) in human beings.
- Consciousness/thought is a means to the end of, i.e., serves, the struggle for existence, in other words, the will; thus, consciousness/thought is biological.
- Such a means tends to develop in excess of its end—and can emancipate itself to become an end-in-itself;
- thus thought can become theoretical (thought about thought) . . .
- . . . and set itself impossible problems (like trying to solve the antimony of mind and matter).
- Such problems can only be solved "by looking backwards, by showing how they arose psychologically within us," i.e. by finding their biological conditions of possibility.
- Therefore, this philosophy is "anti-rational or irrationalist," i.e. not grounded in reason: i.e. . . .
- . . . thought is biological, and . . .
- many thought-processes/-constructs are "consciously false assumptions [as-ifs or fictions], which either contradict reality or are even contradictory in themselves, but which are intentionally thus formed in order to overcome difficulties of thought by this artificial deviation and reach the goal of thought by roundabout ways and by-paths."
- This "un-real" as-if world is as important as the "real" world—in fact, more important in ethical and aesthetic matters.
- Our given reality is our sensations.
- Science deals with the regularities of this reality[; philosophy with the irregularities (?)].
- Much in this reality is fitting [regular], but much is not—but though some of us console ourselves with the fiction that there is a Higher Spirit that created or regulates the universe . . .
- . . . it is senseless [i.e. irrational] to question the meaning of the universe
- a fiction: an assumption known to be false—but useful [a heuristic: "a part of that ars inveniendi which, in former times, was usually appended to Logic" (105)]
- a hypothesis: an assumption that is probable [a provisional idea requiring experiment or evaluation]
- an "arbitrary deviation from reality, that is, . . . contradiction of it"—and, ultimately, self-contradiction (97), which means that . . .
- they "disappear in the course of history [through experience] or through the operation of logic [through thought]" (98),
- they are known to be fictional: "the fiction is just a fiction" (ibid.), and . . .
- . . . expedient: "means to a definite end" (99).
Categories of fiction:
- artificial classification: dichotomy, the Linnaean system
- abstractive (neglective, i.e. reductive) fictions: models, e.g. Adam Smith's assumption that human beings are egoistic, the analogy of psychic phenomena with mechanical processes, etc., linguistic roots, a mean or average (human being), approximation, the Socratic method
- a. schematic fictions, e.g. the simple (isolated) case, b. paradigmatic fictions or imaginary cases, c. utopian fictions, incl. the state of nature, d. the (arche)type
- tropic or symbolic (analogical) fictions, cf. the myth or poetic simile, esp. in physics, metaphysics and theology, e.g. substance, categories, . . .
- juristic (legal) fictions, and . . .
- personificatory fictions: soul, energy, force
- summational fictions (often mnemonic), i.e. general ideas
- heuristic fictions
- practical (ethical) fictions: freedom, the (standpoint of the) ideal
- mathematical fictions: (empty) space, (empty) time, etc.
- abstract generalisation, including mathematical and physical fictions like . . .
- unjustified transference: zero cases, negative/imaginary/irrational numbers, fractions;
- infinity;  matter;  the atom, and other  physical fictions, as well as . . .
- metaphysical fictions [my term] like  the thing-in-itself and  the absolute (17-84)