In aestate calor magnus est, et pueri frigus aquae amant.

The sentence has two clauses joined by et.

• In aestate calor magnus est

  • subject: calor
  • verb: est

• et pueri frigus aquae amant

  • subject: pueri
  • verb: amant
  • direct object: frigus aquae

So Latin is saying, literally, something like:

• In summer, great heat is
• and the boys love the coolness/cold of the water

Because in takes the ablative when it means in, during, or at and shows location or time rather than motion.

So:

• in aestate = in summer / during summer

Here aestate is the ablative singular of aestas, aestatis.

A useful contrast is:

• in + ablative = location/time: in the summer
• in + accusative = motion into: into the summer or into a place

Because magnus is agreeing with calor.

In Latin, adjectives agree with the nouns they describe in:

• gender
• number
• case

Here:

• calor is masculine
• singular
• nominative

So the adjective must also be masculine singular nominative:

• calor magnus = great heat

It is magnus, not magna, because calor is masculine.

Because grammatical gender in Latin is not determined only by the ending you see in the nominative singular.

Calor is a third-declension noun, and its gender is masculine. You usually learn that from the dictionary entry:

• calor, caloris m.

So even though it does not end in -us, it is still masculine, and that is why the adjective is magnus.

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

So a Latin noun like calor can mean:

• heat
• the heat
• sometimes even a heat

The exact sense depends on context.

That is why:

• calor magnus est can be translated as the heat is great or simply heat is great, depending on what sounds natural in English.

Because pueri is nominative plural here, and the nominative case is normally used for the subject.

So:

• pueri = the boys
• amant = love

Together:

• pueri amant = the boys love

A learner may notice that pueri can also be genitive singular in some contexts, but here that would not make sense. Since amant is plural, pueri is clearly the plural subject.

Because its subject, pueri, is plural.

Latin verbs change their endings to match the subject:

• amat = he/she/it loves
• amant = they love

So:

• pueri amant = the boys love

Because the boys are not directly loving water as the object here. They are loving frigus, and aquae depends on frigus.

So the structure is:

• frigus = coldness / coolness
• aquae = of the water

That gives:

• frigus aquae = the coolness of the water / the cold of the water

If the sentence meant the boys love the water, you would expect:

• pueri aquam amant

with aquam as the direct object.

Here aquae is genitive singular.

It depends on frigus and answers the question coolness/coldness of what?

• frigus aquae = the coolness of the water

You know it is genitive here because:

1. that construction makes good sense grammatically
2. frigus often takes a dependent genitive like this
3. aquae as nominative plural would mean waters, which would not fit the sentence as well

So in this context, aquae is best understood as of water or of the water.

Yes. Literally, it is the coldness/coolness of the water.

Depending on context, a more natural English translation might be:

• the coolness of the water
• the cold water, if translating loosely
• the refreshing cool of the water

But grammatically, Latin is using a noun phrase:

• frigus
  • aquae
• coolness/coldness
  • of water

It is not using an adjective like frigida aqua (cold water).

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

So this sentence could be rearranged in various ways without changing the basic meaning, for example:

• Calor magnus in aestate est, et pueri frigus aquae amant.
• In aestate magnus calor est, et pueri aquae frigus amant.

The original order is perfectly normal, but not the only possible order.

English depends heavily on word order for meaning. Latin depends much more on case endings and verb endings.

They come from several different declensions:

• aestas, aestatis = third declension
• calor, caloris = third declension
• puer, pueri = second declension
• frigus, frigoris = third declension, neuter
• aqua, aquae = first declension

This is a good example of how one short Latin sentence can mix several declensions at once.