Category is a philosophical term that has been given many different meanings by different thinkers. In Aristotelian philosophy (see Aristotle), it signifies one of the ultimate classes (e.g., substance, quality, quantity, relation) to which things can be referred. Thus an object might be of the substance, table; the quality, brown, and so on. In the philosophy of Kant, however, the categories are the a priori concepts in terms of which the human mind organizes and interprets its experience of the world. The notions of cause and substance are Kantian categories.