Knowledge necessarily uses fictions!

I’m about on third of the way through Hans Vaihinger’s Philosophy of As If. I believe he is overall correct. I may differ on some details. E.g. even in Principia Mathematica classes are logical fictions. I suspect beyond even that Predicates (including relations) are also fictions. As is anything that can be named or described! Mind & Matter are both fictions. Only instances of immediate experience are real – but they cannot be named or described!