Greek word for custom or habit, the characteristic conduct of an individual human life. Hence, beginning with Aristotle , ethics is the study of human conduct. Also see PP . A straight line can be extended indefinitely in either direction. From a center point, a circle can be drawn with any radius.
All right angles are equal to each other.
If two straight lines crossing a third form angles less than two right angles on one of its sides, then indefinite extensions of these lines eventually meet. Although rejection of the fifth postulate eventually led to the development of alternative geometries by Lobachevsky and Riemann , Euclid's emphasis on axiomatic structure remained significant for mathematicians like Peano and Hilbert and served as a significant model for such philosophers as Hobbes and Spinoza . Kant condemned this approach to human conduct as heteronomous . Also see ISM , Ralph Nicholas Wedgewood , OCP , and PP . Also see Paul Golba , David Wilkins , TTSB , and MMT .