When is quis used instead of aliquis?

Question

I definitely remember that one usually says: si quis veniret … and not: si aliquis veniret. But the recent question about quo quisque est sollertior and similar forms brought the following rule from Allen & Greenough to my attention:

The indefinite quis is rare except in the combinations sī quis (if any), nisi quis (if any . . . not), nē quis (lest any, in order that none), num quis (ecquis whether any) and in relative clauses.

(§ 310 no. 2)

Si, nisi, ne, num are certainly uncontroversial, but I seem to remember that there was a longer list, so I looked it up in my pocket grammar (Langenscheidts Kurzgrammatik Latein, if you must know), and indeed it lists the following words calling for the ali-less pronoun: si, nisi, ne, num, quo, quanto, cum. And google-ing further, I also found other lists, such as: si, nisi, ne, num, quo, ubi, quando, cum.

And indeed I find, for example, this from Cicero (Pro Rabirio postumo 36):

Ubi semel quis peieraverit, ei credi postea, etiam si per pluris deos iuret, non oportet.
Once somebody has sworn falsely, one must not believe him any more, even if he should swear by multiple gods.

It is generally understood that in all cases where you can say quis (or quid), you can generally also say aliquis (or aliquid) for emphasis. But where is it permissible (and needed, unless one wants to express emphasis) to leave out the ali- prefix?

Answer 1

It's not generally permissible to substitute quis for aliquis, because quis functions as an interrogative when it's not bound in a subordinate clause that makes that meaning impossible. Aliquis venit means "someone is coming". Quis venit means "who is coming?"

Quis venit? Aliquis venit. is a conversation, if a frustrating one.

Quis venit? QUIS venit is the start of a bad comedy sketch...much inferior to Quis in primo?

Not only can you not use quis as an indefinite in a main clause, you also can't in a subordinate clause that could be an indirect question.

Note also that si aliquis is not the only alternative to si quis. Quicumque ("whosoever"), alternatively quicunque, also works if the same indefinite person will be the subject of the main clause verb also. So sentences ending in anathema sit might start with any of si quis, si aliquis, quicumque, quicunque.

Magna Carta uses all of si quis, si aliquis, and quicumque. Interestingly, at first glance it seems to prefer aliquis not for emphasis, but when an adjective is needed, as Si aliquis liber homo.

Getting back to the original question, if you are a native English speaker, the traditional translations of indefinite quis as "anyone" and aliquis as "someone" should be helpful to keep in mind, though not always to be taken literally in places where you could use either form in Latin. Certainly I would not translate si aliquis liber homo as "if some free man" but as "if any free man".