Although on the face of it the difference between pretending that something is so, and actually supposing that it is so, is clear enough, it can come under pressure. Philosophies such as fictionalism (see Vaihinger) or constructive empiricism, quasi-realism, and instrumentalism, counsel that we think of some commitments as useful tools rather than as strict representations of how things are. But taking them in that spirit comes close to believing them, just as pretending to be a window-cleaner, convincingly enough, comes close to cleaning windows.