The difference between coniunctivus and imperativus when expressing commands

Question

What is the rule for choosing coniunctivus or imperativus when expressing commands? I know, that imperativus has only second person forms, so one is forced to use coniunctivus for other persons. Are there other rules however that make sentences with these modes different?

Answer 1

Hmm. My understanding is that the bare subjunctive as a positive request/command is actually rather rare in classical Latin. Woodcock's New Latin Syntax, p. 97, after a discussion of noli, nolite + infinitive as more polite than ne + perfect subjunctive, tells us:

Besides noli, nolite with the infinitive, the following periphrases also are frequently employed for the sake of politeness: (i) For positive commands, fac, facite, with a quasi-subordinate subjunctive: Fac mihi scribas; facite mihi scribatis, "See that you write to me." The subordinating conjunction ut is usually omitted. Similarly vide, "see that . . .", and velim, "I should like . . ." are used with the subjunctive: Plaut Asin 755 scribas vide plane et probe, "see that you write clearly and properly"; Cic. Fam. 9, 12, 2 tu velim animo forti sis, "I should like you to be of brave heart." (ii) For negative commands fac ne . . ., facite ne . . ., and vide ne . . . are used. Rather more frequent are cave (sometimes caveto) and cavete with, or more often without, ne: Plaut. Most. 324 cave ne cadas, "mind you don't fall"; Cic. Att. 3, 17, 3 cave vereare, "mind you don't fear."

Answer 2

If you really want to give a command, use imperative. If you want to request someone to do something, use conjunctive. The difference between curre and curras is similar to the difference between "run" and "please run".