Other philosophers have defined persons in different ways.

Various philosophers define the doctrine in various ways, but all definitions generally revolve around a moral obligation to benefit others or the pronouncement of moral value in serving others rather than oneself.

Greek philosophers defined a number of syllogisms, correct three part inferences, that can be used as building blocks for more complex reasoning.

Ancient Greek and Indian philosophers defined music as tones ordered horizontally as melodies and vertically as harmonies.

Nonetheless, some philosophers have defined free will as the absence of various impediments.

Moral philosophers have defined discrimination as disadvantageous treatment or consideration.

The Church and some philosophers define relativism as the denial of absolute truth.

In philosophy, the study of knowledge is called epistemology; the philosopher Plato famously defined knowledge as "justified true belief."

Later Greek philosophers defined the classic five simple machines (excluding the inclined plane) and were able to roughly calculate their mechanical advantage.