Aqua pura et quies aegrotis prosunt; clamor autem nimius eis obest.

Because the subject is compound: aqua pura et quies = pure water and rest. Two singular nouns joined by et normally take a plural verb in Latin, so prosunt means they are beneficial / they help.

Aegrotis is dative plural of aegrotus, meaning to the sick / for the sick.

The verb prosum (prosunt here) takes the dative of the person who receives the benefit. So:

• aqua pura et quies aegrotis prosunt
• literally: pure water and rest are beneficial to the sick

This is different from English, where we often just say help the sick.

Eis is also dative plural, meaning to them. It refers back to aegrotis.

So the sentence first says to the sick, then later says to them rather than repeating the noun. Latin often does this just as English does:

• Pure water and rest help the sick; excessive noise, however, harms them.

Using eis avoids repetition and makes the second clause flow more naturally.

Yes. Both verbs take a dative object.

• prosum, prodesse = to be useful to / help
• obsum, obesse = to be harmful to / harm

So:

• aegrotis prosunt = they help the sick
• eis obest = it harms them

A learner should remember these as verbs that regularly govern the dative.

Because the subjects are different.

• prosunt has the compound subject aqua pura et quies → plural verb
• obest has the singular subject clamor nimius → singular verb

So the number of the verb matches the number of its subject.

Quies means rest or quiet/restfulness. Here it is nominative singular, and it is one of the two subjects of prosunt.

So the structure is:

• aqua pura = one subject
• quies = second subject
• prosunt = plural verb for both together

Pura is an adjective agreeing with aqua.

• aqua is feminine singular nominative
• so pura is also feminine singular nominative

Latin adjectives must agree with the nouns they modify in gender, number, and case.

Nimius agrees with clamor.

• clamor is masculine singular nominative
• so nimius is also masculine singular nominative

Together they mean excessive noise.

Autem is a postpositive word in Latin. That means it usually comes second in its clause, not first.

So Latin prefers:

• clamor autem nimius

rather than:

• autem clamor nimius

It often means however, but, or on the other hand.

Both can mark contrast, but they are not identical.

• sed often gives a more direct but
• autem often gives a softer contrast: however, on the other hand

Here autem suits the balanced contrast between the two clauses:

• pure water and rest help the sick;
• excessive noise, however, harms them.

Latin word order is much freer than English word order because the endings show the grammatical relationships.

This sentence is arranged for style and emphasis:

• Aqua pura et quies first: the beneficial things
• aegrotis before prosunt: the people affected
• then a contrasting second clause
• autem marks the turn
• obest comes at the end, which is very natural in Latin

So the sentence is not random; it is flexible but meaningful.

Yes, Latin could have omitted eis if the meaning were clear from context:

• Aqua pura et quies aegrotis prosunt; clamor autem nimius obest.

That would still make sense: Pure water and rest help the sick; excessive noise, however, is harmful.

But eis makes the reference explicit: harmful to them.

Latin has no articles like English the or a/an. Whether a noun is definite or indefinite must be understood from context.

So:

• aqua pura can mean pure water or the pure water, depending on context
• aegrotis can mean to sick people or to the sick

In this sentence, English naturally supplies the sick.

Formally, aegrotis comes from the adjective aegrotus = sick. But here it is being used substantively, meaning sick people or the sick.

Latin does this very often:

• boni = the good
• mali = the bad
• aegroti = the sick

So aegrotis literally means to sick ones, but in natural English we say to the sick.

A useful set of dictionary forms would be:

• aqua, aquae — water
• purus, pura, purum — pure
• et — and
• quies, quietis — rest
• aegrotus, aegrota, aegrotum — sick
• prosum, prodesse, profui — be useful to, help
• clamor, clamoris — noise, shouting
• autem — however, but
• nimius, nimia, nimium — excessive
• is, ea, id — he, she, it; that
• obsum, obesse, obfui — be harmful to, harm

Notice especially that prosunt comes from prosum and obest comes from obsum.

They are compounds of sum:

• pro + sum → prosum
• ob + sum → obsum

Because they are built from sum, their forms follow sum:

• prosum, prodes, prodest, prosumus, prodestis, prosunt
• obsum, obes, obest, obsumus, obestis, obsunt

So prosunt and obest may look unusual at first, but they make more sense once you know they are compounds of sum.