§§30--36. Summary. With respect to physical science, we might urge that nature has constructed man with great art. His mind is naturally formed for the attainment of knowledge (30). For this purpose the mind uses the senses, and so gradually arrives at virtue, which is the perfection of the reason. Those then who deny that any certainty can be attained through the senses, throw the whole of life into confusion (31). Some sceptics say "we cannot help it." Others distinguish between the absolute absence of certainty, and the denial of its absolute presence. Let us deal with these rather than with the former (32). Now they on the one hand profess to distinguish between true and false, and on the other hold that no absolutely certain method for distinguishing between true and false is possible (33). This is absurd, a thing cannot be known at all unless by such marks as can appertain to no other thing. How can a thing be said to be "evidently white," if the possibility remains that it may be really black? Again, how can a thing be "evident" at all if it may be after all a mere phantom (34)? There is no definite mark, say the sceptics, by which a thing may be known. Their "probability" then is mere random guess work (35). Even if they only profess to decide after careful pondering of the circumstances, we reply that a decision which is still possibly false is useless (36). §30. _Physicis_: neuter not masc.; cf. I. 6. _Libertatem et licentiam_: _et_ = "and even." _Libertas_ = παρρησια as often in Tacitus. _Abditis rebus et obscuris_: cf. n. on I. 15, and the word συνεσκιασμενος Sext. _Adv. Math._ VII. 26. _Lucem eripere_: like _tollere_ (n. on 26), cf. 38, 103 and _N.D._ I. 6. For the sense see n. on 16, also 61. _Artificio_: this word is used in Cic. as equivalent to _ars_ in all its senses, cf. 114 and _De Or._ II. 83. _Fabricata esset_: the expression is sneered at in 87. _Quem ad modum primum_: so Halm rightly for MSS. _prima_ or _primo_, which latter is not often followed by _deinde_ in Cicero. _Primum_ is out of position, as in 24. _Appetitio pulsa_: = _mota_, set in motion. For ‛ορμη see 24. _Intenderemus_: as in the exx. given in 20. _Fons_: "reservoir," rather than "source" here. It will be noted that συγκαταθεσις must take place before the ‛ορμη is roused. _Ipse sensus est_: an approach to this theory is made in Plat. _Theaet._ 185, 191. Cf. especially Sext. _Adv. Math._ VII. 350 και ‛οι μεν διαφερειν αυτην των αισθησεων, ‛ως ‛οι πλειους, ‛οι δε αυτην ειναι τας αισθησεις ... ‛ης στασεως ηρξε Στρατον. All powers of sensation with the Stoics, who are perhaps imitated here, were included in the ‛ηγεμονικον, cf. n. on I. 38. _Alia quasi_: so Faber for _aliqua_. "_In vera et aperta partitione nec Cicero nec alius quisquam aliquis--alius dixit, multo minus alius--aliquis_," _M.D.F._ III. 63. Goer. on the other hand says he can produce 50 exx.