hexis (Greek, from hexo, ‘to have’, ‘to be disposed’), a (good or bad) condition, disposition, or state. The traditional rendering, ‘habit’ (Latin habitus), is misleading, for it tends to suggest the idea of an involuntary and merely repetitious pattern of behavior. A hexis is rather a state of character or of mind that disposes us to deliberately choose to act or to think in a certain way. The term acquired a quasi-technical status after Aristotle advanced the view that hexis is the genus of virtue, both moral and intellectual. In the Nicomachean Ethics he distinguishes hexeis from passions (pathe) and faculties (dunamis) of the soul. If a man fighting in the front ranks feels afraid when he sees the enemy approaching, he is undergoing an involuntary passion. His capacity to be affected by fear on this or other occasions is part of his makeup, one of his faculties. If he chooses to stay where his commanders placed him, this is due to the hexis or state of character we call courage. Likewise, one who is consistently good at identifying what is best for oneself can be said to possess a hexis called prudence. Not all states and dispositions are commendable. Cowardice and stupidity are also hexeis. Both in the sense of ‘state’ and of ‘possession’ hexis plays a role in Aristotle’s Categories. See also ARISTOTLE , VIRTUE ETHICS. A.G.-L. Heytesbury, William, also called Hentisberus, Hentisberi, Tisberi (before 1313–c.1372), English philosopher and chancellor of Oxford University. He wrote Sophismata (‘Sophisms’), Regulae solvendi sophismata (‘Rules for Solving Sophisms’), and De sensu composito et diviso (‘On the Composite and Divided Sense’). Other works are doubtfully attributed to him. Heytesbury belonged to the generation immediately after Thomas Bradwardine and Kilvington, and was among the most significant members of the Oxford Calculators, important in the early developemnt of physics. Unlike Kilvington but like Bradwardine, he appealed to mathematical calculations in addition to logical and conceptual analysis in the treatment of change, motion, acceleration, and other physical notions. His Regulae includes perhaps the most influential treatment of the liar paradox in the Middle Ages. Heytesbury’s work makes widespread use of ‘imaginary’ thought experiments assuming physical impossibilities that are yet logically consistent. His influence was especially strong in Italy in the fifteenth century, where his works were studied widely and commented on many times. See also OXFORD CALCULATORS. P.V.S.