Pater aquam pro vino bibit.

Because aquam is the accusative singular of aqua (water).

In this sentence, aquam is the direct object of bibit (drinks / drank), so Latin uses the accusative case. A native English speaker may not expect this, because English usually shows the object mainly by word order, not by changing the noun ending.

• aqua = water
• aquam = water as the object

So Pater aquam ... bibit means Father drinks/drank water.

Because pro takes the ablative case, and the ablative singular of vinum is vino.

So:

• vinum = wine
• vino = with/for/in place of wine, depending on context

In this sentence, pro vino means instead of wine or in place of wine.

That is why Latin says pro vino, not pro vinum.

Here pro means instead of or in place of.

So aquam pro vino bibit means that the father drinks water instead of wine.

This is a very common use of pro with the ablative. In other contexts, pro can also mean things like for, on behalf of, or in front of, but in this sentence instead of is the natural meaning.

Because pater is the subject of the sentence, so it is in the nominative case.

Latin marks the subject by case ending rather than by position alone.

• pater = father as the subject
• patrem = father as the direct object

So in Pater aquam pro vino bibit, pater is the one doing the drinking.

It can mean either drinks or drank, depending on context.

The form bibit can be:

• present tense: he/she drinks
• perfect tense: he/she drank / has drunk

In an isolated sentence like this, many beginners are taught to take it as drinks, unless context suggests otherwise.

So the sentence can be understood as:

• Father drinks water instead of wine or
• Father drank water instead of wine

We know from two things:

1. pater is in the nominative, which marks the subject.
2. bibit is third person singular, meaning he/she drinks or he/she drank.

Since pater is a singular noun and is nominative, it matches the verb as the subject.

So pater is the one who drinks.

Yes. Latin word order is more flexible than English because the endings show each word’s function.

For example, these would mean essentially the same thing:

• Pater aquam pro vino bibit
• Aquam pater pro vino bibit
• Pro vino pater aquam bibit

The basic meaning stays the same because:

• pater is nominative
• aquam is accusative
• vino is ablative after pro

However, changing the word order can change the emphasis. For example, starting with aquam may emphasize water.

Because Latin often does not use articles like English the and a/an.

So pater can mean:

• father
• the father
• a father

Likewise aquam can mean water, the water, or sometimes some water, depending on context.

Latin usually leaves that detail for the reader to infer from the situation.

It is most naturally understood with the whole action of drinking: he drinks water instead of wine.

In other words, pro vino tells us the role of water in the event: the water is being drunk in place of wine.

So although it is closely related in meaning to aquam, it works as a prepositional phrase within the sentence as a whole.

The dictionary forms are:

• pater from pater, patris = father
• aquam from aqua, aquae = water
• pro = for, on behalf of, instead of; takes the ablative
• vino from vinum, vini = wine
• bibit from bibo, bibere, bibi = drink

A learner often needs to know the dictionary form in order to recognize how the word has changed in the sentence.