§ 31-32 Consider the geography of the Aegean. Philip undertakes enterprises in the North at seasons when natural causes prevent our moving thither (31). We must therefore have a permanent force in the North to reach him easily (32).
τὸν τόπον, ‘the geographical position.’
πνεύμασιν and ὥραις are instrumental with προλαμβάνων. ‘Philip generally effects his object by making use of the winds and the seasons to get the start of you.’ The following clause coupled to this by καὶ (almost=‘that is’) gives the same sense in a more definite form.
φυλάξας, ‘watching (and waiting) for’ (like τηρεῖν in Thuc. III.22 and elsewhere). Cf. Antiphon 145. 48.
τοὺς ἐτησίας, sc. ἀνέμους, ‘the annual winds’ or ‘trade-winds’ which blew from the North over the Aegean from the end of July to the end of September, and would therefore impede the Athenians in any attempt to reach Macedonia or their possessions near Macedonia. In winter the use of ships, and indeed almost any warlike operation, was practically suspended in Greece.
ἂν, with δυναίμεθα, a condition (e.g. εἰ δέοι) being implied. (See on § 18 εἰ μὴ ποιήσαιτ᾽ ἄν.) The negative is μὴ because of the idea of purpose in the clause: in a relative clause expressing purpose, as in many other cases, the optative with ἂν is almost equivalent to the future indicative.