- A priori knowledge or justification is independent of experience (for example "All bachelors are unmarried"). Galen Strawson has stated that an a priori argument is one in which "you can see that it is true just lying on your couch. You don't have to get up off your couch and go outside and examine the way things are in the physical world. You don't have to do any science.";
- A posteriori knowledge or justification is dependent on experience or empirical evidence (for example "Some bachelors are very unhappy").
An a priori language is any constructed language whose vocabulary is not based on existing languages, unlike a posteriori constructed languages. Examples of a priori languages include Lojban, Loglan, Ro, Solresol, Mirad, Klingon, Ithkuil, Na'vi, and High Valyrian. By contrast, a posteriori languages are ones whose vocabulary is based on existing languages, either as a variation of one language (e.g., Latino sine flexione) or as a mixture of various languages (e.g., Esperanto).
- Sommers, Tamler (2003)