while sensations and feelings are real, the rest of human knowledge consists of “fictions” that can only be justified pragmatically.
In his view, even the laws of logic are fictions, albeit fictions that have proved their indispensable worth in experience and are thus held to be undeniably true. Vaihinger believes that it is not worth asking whether ethical, religious and metaphysical doctrines are true in an objective sense, since this cannot be discovered, but that one should ask whether it is useful or even necessary to act ‘as if’ they were true.
(For example, according to Kantian ethics, we must act ‘as if’ moral laws were laws of nature because of our non-physical consciences.)
He concedes that the concepts of fiction and ‘as if’ vary depending on the type of truth concerned, which may be logical, scientific, religious, or something else.