When something is patently true, or patently false, you mean it is very clear — so clear that arguing the other way starts to look dishonest. English likes it in front of words such as obvious, false, absurd, unfair. It is a little formal and a little sharp: you are not only saying “clearly”; you are saying “look, it is sitting there in the open.” You hear it in news, essays, and annoyed talk among people who read a lot, not from small children. Though actually, it does not come from the inventor’s patent. The adverb is patent (the old adjective meaning “open, plain to see”) plus -ly. That patent and the legal patent share an older idea of something lying open, where anyone can look; in real use, patently belongs with “obvious,” not with “inventions.”