Subject in question, as to assert or deny the truth either of the Peripatetick, or the Chymical Doctrine concerning the number of the Elements, but only to shew you that neither of these Doctrines hath been satisfactorily proved by the arguments commonly alledged on its behalfe. So that if I really discern (as perhaps I think I do) that there may be a more rational account then ordinary, given of one of these opinions, I am left free to declare my self of it, notwithstanding my present engagement, it being obvious to all your observation, that a solid truth may be generally maintained by no other, then incompetent Arguments. And to this Declaration I hope it will be needless to add, that my task obliges me not to answer the Arguments that may be drawn either for _Themistius_ or _Philoponus's_ Opinion from the Topick of reason, as opposed to experiments; since 'tis these only that I am to examine and not all these neither, but such of them alone as either of them shall think fit to insist on, and as have hitherto been wont to be brought either to prove that 'tis the four Peripatetick Elements, or that 'tis the three Chymical Principles that all compounded bodies consist of. These things (adds _Carneades_) I thought my self obliged to premise, partly lest you should do these Gentlemen (pointing at _Themistius_ and _Philoponus_, and smiling on them) the injury of measuring their parts by the arguments they are ready to propose, the lawes of our Conference confining them to make use of those that the vulgar of Philosophers (for even of them there is a vulgar) has drawn up to their hands; and partly, that you should not condemn me of presumption for disputing against persons over whom I can hope for no advantage, that _I_ must not derive from the nature, or rules of our controversy, wherein I have but a negative to defend, and wherein too I am like on several occasions to have the Assistance of one of my disagreeing adversaries against the other.