The terms a priori (“from the earlier”) and a posteriori (“from the later”) are used in philosophy (epistemology) to distinguish two types of knowledge, justification, or argument: 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 I have met are very happy”). There are many points of view on these two types of knowledge, and their relationship is one of the oldest problems in modern philosophy. The terms a priori and a posteriori are primarily used as adjectives to modify the noun “knowledge” (for example, “a priori knowledge”). However, “a priori” is sometimes used to modify other nouns, such as “truth”. Philosophers also may use “apriority” and “aprioricity” as nouns to refer (approximately) to the quality of being “a priori”. Although definitions and use of the terms have varied in the history of philosophy, they have consistently labeled two separate epistemological notions.