  Euclid (fl. 300 BCE) placed at the head of his Elements a series of ‘definitions’ (e.g., “A point is that which has no part”) and ‘common notions’ (e.g., “If equals be added to equals, the sums are equal”), and five ‘requests’. Supposedly these items conveyed all of the information needed for inferring the theorems and solving the problems of geometry, but as a matter of fact they do not. However, the requests (aitemata)—usually called ‘postulates’ in English—must at any rate be granted or Euclid's proofs will not go through. Some of them are plainly practical: