a given subject exists; next, if it does exist, what is its real constituent essence or definition. We thus see the reason for the order in which Aristotle has arranged the two co-ordinate pairs of _Quæsita_ or Problems, conformable to the different processes pursued, on the one hand, by the common intellect, growing and untrained--on the other, by the mature or disciplined intellect, already competent for philosophical exposition and applying itself to new _incognita_. [Footnote 2: **Schol. Philopon. p. 241, a. 18-24: [Greek: tou/tôn to\ ei) e)/sti kai\ to\ ti/ e)stin ei)si\n a(pla=, to\ de\ o(/ti kai\ to\ dio/ti su/ntheta--pro/tera ga\r ê(mi=n kai\ gnôrimô/tera ta\ su/ntheta, ô(s tê=| phu/sei ta\ a(pla=.] Mr. Poste observes upon this quadruple classification by Aristotle (p. 96):--"The two last of these are problems of Inductive, but first principles of Deductive, Science; the one being the hypothesis, the other the definition. The **attribute as well as the subject must be defined (I. x.), so that to a certain degree the second problem also is assumed among the principles of Demonstration."] Comparing together these four _Quæsita_, it will appear that in the first and third (_Quod_ and _An_), we seek to find out whether there is or is not any middle term. In the second and fourth (_Cur_ and _Quid_), we already know or assume that there is a middle term; and we try to ascertain what that middle term is.[3] The enquiry _Cur_, is in the main analogous to the enquiry _Quid_; in both cases, we aim at ascertaining what the cause or middle term is. But, in the enquiry _Cur_, what we discover is perhaps some independent fact or event, which is the cause of the event _quæsitum_; while, in the enquiry _Quid_, what we seek is the real essence or definition of the substance--the fundamental, generating, immanent cause of its concomitant attributes. Sometimes, however, the _Quid_ and the _Cur_ are only different ways of stating the same thing. _E.g._, _Quid est eclipsis lunæ_? Answer: The essence of an eclipse is a privation of light from the moon, through intervention of the earth between her and the sun. _Cur locum habet eclipsis lunæ_? Answer: Because the light of the sun is prevented from reaching the moon by intervention of the earth. Here it is manifest that the answers to the enquiries _Quid_ and _Cur_ are really and in substance the same fact, only stated in different phrases.[4] [Footnote 3: Analyt. Post. II. i. p. 889, b. 37-p. 90, a. 7. [Greek: sumbai/nei a)/ra e)n a(pa/sais tai=s zêtê/sesi zêtei=n ê)\ ei) e)/sti me/son, ê)\ ti/ e)sti to\ me/son; to\ me\n ga\r ai)/tion to\ me/son, e)n a(/pasi de\ tou=to zêtei=tai.] Compare Schol. p. 241, b. 10, Br.] [Footnote 4: Analyt. Post. II. ii. p. 90, a. 14-23, 31: [Greek: to\ ti/ e)stin ei)de/nai tau)to/ e)sti kai\ dia\ ti/ e)stin.]]