In Analytica Posteriora Aristotle introduces two types of demonstrations, that is, apodeixis tou di-oti and apodeixis tou hoti. His examples are as follows: for the former, "What is near does not twinkle. The planets are near. Therefore the planets do not twinkle."; for the latter, "What does not twinkle is near. The planets do not twinkle. Therefore the planets are near." (78a 30-78b 2) The former establishes the reason, for the planets do not twinkle, because they are near, but not the converse. Thus Aristotle's explanation is a deduction of the immediate fact (not twinkling) through the remote cause (nearness). If we want to explain something, we start from established facts, then we look for a reason able to deduce them. This feature of Aristotelian explanation is combined with his notion of conditional necessity. He says often "if a house has come about it is necessary for stones to have been cut down and to have come about". (An. Post. 95b 33-34) But we cannot say the converse, because it is not necessary for a house to have come about, even though a foundation has come about. Consequently, "it is necessary to begin from something that is immediate and first (reckoning back) from the present". We must search for the cause of facts in the past, because the future is not accomplished and indeteminate. This kind of explanation may be called retrospective explanation, and it does not intend to provide any prediction. This retrospective explanation constitutes Aristotelian conceptual framework which was broken in the 17th century. The modern science was born, when the vector of explanation was converted into the future.