Pairs of words that work together across a clause: et … et "both … and", nec … nec "neither … nor", vel … vel, aut … aut "either … or", sive … sive "whether … or", cum … tum "both … and especially", non tam … quam "not so much … as".
When you meet et, nec, vel, aut, sive or cum, look ahead for a second one. If there is one, the first means "both", "neither", "either" or "whether", not "and", "nor", "or": nec bona … nec mala "neither good nor bad".
cum … tum "both … and especially": when a tum follows, the cum is not "when" or "since".
non tam … quam "not so much … as"; tam … quam "as … as"; sicut … ita and ut … ita "as … so", "just as … so also".
neque enim is "for … not", not the first half of a pair: neque enim aut praeteritum aut futurum amittere quis potest "for no one can lose either the past or the future".