Authors/Ockham/Summa Logicae/Book III-2/Chapter 41

Latin	English
CAP. 41. QUOMODO TERMINATUR QUAESTIO ‘QUID EST’?.	Chapter 41, How the question 'quid est' (what is?) is settled?
Per praedicta potest faciliter sciri quomodo terminatur quaestio ‘quid est’. Dupliciter enim potest terminari, scilicet per experientiam et intuitivam notitiam, sicut si aliquis videret terram interponi inter solem et lunam. Aliter potest terminari a posteriori per effectum et per demonstrationem, quia sicut astrologus, sciens quod luna illuminatur a sole nisi sit aliquod opacum medium et sciens quod nullum aliud a terra est medium, concludit quod terra interponitur inter solem et lunam et quod illa interpositio est causa eclipsis.	Through the foregoing it can be easily understood how the question 'what is' is settled. For it can be determined in two ways, that is, by experience and intuitive knowledge, as if one saw the earth interposed between the sun and the moon. It can be concluded differently from the latter by effect and by demonstration, because like an astrologer, knowing that the moon is illuminated by the sun unless there is some opaque object as the medium and knowing that there is no medium other than the earth, he concludes that the earth is interposed between the sun and the moon and that this interposition is the cause of the eclipse.
Et sicut est de ista causa, ita est de multis aliis principiis, quod dupliciter notificari possunt; et ita talia principia, quantumcumque sint dubitabilia, tamen demonstrari non possunt a priori, licet quaedam demonstrari possint a posteriori, propter quod in demonstrationibus non est circulus. Quaedam enim principia nec a priori nec a posteriori demonstrari possunt, cuiusmodi sunt principia per se nota quae cognoscuntur cognitis terminis et quaedam alia principia prima quae nonnisi per experientiam et nullo modo per effectus evidenter sciri possunt. Quaedam autem principia licet possint a posteriori demonstrari, tamen talis demonstrans per illud principium --- nisi aliunde adquirat notitiam eiusdem --- non demonstrabit conclusionem.	And as it is of this cause, so it is of many other principles, which may be known in two ways; and thus such principles, no matter how doubtful they may be, yet cannot be demonstrated a priori, although some can be demonstrated a posteriori, for which reason there is no circle in demonstrations. For certain principles can be demonstrated neither a priori nor a posteriori, such as principles known by themselves which are known by known terms, and certain other first principles which can only be clearly known through experience and in no way through effects. Now, although some principles may be demonstrated from the latter, yet such a one demonstrating by means of that principle --- unless he acquires knowledge of the same from elsewhere --- will not demonstrate the conclusion.
Et ita possibile est, ƿ quod unus per principia demonstret conclusionem et alius per conclusionem demonstret principium a posteriori, tamen idem simul et semel non potest hoc facere.	And so it is possible, that one person demonstrates the conclusion by principles and another demonstrates the principle by means of the conclusion, yet the same cannot do this at the same time and at once.
Et ista de demonstratione sufficiant. Tantum enim ad completionem istius Summae, ne liber Posteriorum totaliter dimitteretur intactus, tractatum de demonstratione inserui, multa quae sunt hic omissa in expositione Posteriorum Aristotelis explicaturus.	And these are enough on demonstration. For it was only to complete this Summa, that the book of the Posteriors might not be dismissed entirely untouched, that I inserted a treatise on demonstration, many of which were omitted here in the exposition of the Posteriors, which Aristotle intended to explain.