Puer caudam canis tangit, sed canis quietus manet.

Because puer is in the nominative case, which is the case normally used for the subject of a sentence.

• puer = boy
• tangit = he/she/it touches

So Puer tangit means The boy touches.

Also, puer is a very common second-declension masculine noun with the slightly unusual dictionary form ending in -er rather than -us.

Because caudam is the direct object of tangit. It is the thing being touched, so it must be in the accusative singular.

• nominative: cauda = tail
• accusative: caudam = tail as the object

So:

• cauda = a tail / the tail as subject
• caudam = a tail / the tail as object

In this sentence, the boy is doing the touching, and the tail is receiving the action, so Latin uses caudam.

Because the form canis can be either:

• nominative singular = dog
• genitive singular = of the dog

This is normal for some third-declension nouns.

So in this sentence:

• caudam canis = the dog's tail / the tail of the dog
  Here canis is genitive singular.
• sed canis quietus manet = but the dog remains calm
  Here canis is nominative singular.

You tell which it is by its job in the sentence, not just by its form.

Because it is attached to caudam and shows possession:

• caudam canis = the tail of the dog

A native English speaker may expect something like dog's tail, but Latin often expresses that idea with a genitive noun after the thing possessed.

So:

• cauda canis = the dog's tail
• literally: tail of the dog

The context makes this very clear: the boy is not touching the dog directly here; he is touching the dog's tail.

Because quietus is describing canis, and it must agree with canis in:

• gender: masculine
• number: singular
• case: nominative

Since canis here is nominative singular masculine, the adjective must also be nominative singular masculine:

• quietus = masculine nominative singular
• quieta = feminine nominative singular
• quietum = masculine accusative singular or neuter nominative/accusative singular, depending on context

So canis quietus means the dog, calm or more naturally the calm dog / the dog is calm, depending on the sentence structure.

Because after verbs like manet (remains), Latin often uses a predicate adjective in the nominative to describe the subject.

So:

• canis = subject, nominative
• quietus = adjective describing the subject, also nominative

This is similar to English The dog remains calm, where calm describes dog, not a separate object.

Latin does not treat quietus as an object here.

Manet means remains, stays, or continues to be.

It comes from manere, meaning to remain.

So:

• canis quietus manet = the dog remains calm/quiet

This suggests that even though the boy touches the dog's tail, the dog does not react aggressively or excitedly. It stays calm.

Because Latin has no articles like English the and a/an.

So a noun like puer can mean:

• a boy
• the boy

and canis can mean:

• a dog
• the dog

You decide from the context which is most natural in English.

In this sentence, English usually translates it with the:

• The boy touches the dog's tail, but the dog remains calm.

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

Both of these could express the dog's tail:

• caudam canis
• canis caudam

The version in your sentence puts caudam first, which may slightly emphasize the thing being touched before identifying whose tail it is.

A useful point for learners: in Latin, you should rely more on cases than on word order.

Yes, but that would mean something different:

• Puer canem tangit = The boy touches the dog
• Puer caudam canis tangit = The boy touches the dog's tail

So the sentence you have is more specific. The object is not the whole dog, but the tail.

Tangit is:

• present tense
• third person singular
• from tangere = to touch

So it means:

• he touches
• she touches
• it touches

Here, because the subject is puer, it means the boy touches.

Manet is:

• present tense
• third person singular
• from manere = to remain

So it means:

• he remains
• she remains
• it remains

Here the subject is canis, so it means the dog remains.

Sed means but.

It connects the two parts of the sentence:

• Puer caudam canis tangit = The boy touches the dog's tail
• sed canis quietus manet = but the dog remains calm

So sed introduces a contrast: you might expect the dog to react, but it stays calm.

In this sentence, calm is usually the better English choice.

Why? Because in English, quiet often refers to not making noise, while calm suggests not getting upset or agitated. Since the dog is having its tail touched, the idea is probably that it stays calm.

Still, quiet is not impossible depending on the context. Latin adjectives often cover a range of meanings, and the best English translation depends on what sounds natural in context.

A simple breakdown is:

• Puer — nominative singular, subject: the boy
• caudam — accusative singular, direct object: tail
• canis — genitive singular: of the dog
• tangit — verb: touches
• sed — conjunction: but
• canis — nominative singular, subject: the dog
• quietus — nominative singular masculine adjective agreeing with canis: calm
• manet — verb: remains

So the structure is:

• [Subject] [Object + possessor] [Verb], but [Subject] [predicate adjective] [Verb].

Because manet already means remains and links the subject to its description.

Latin often does this with verbs like:

• esse = to be
• manere = to remain
• videri = to seem

So canis quietus manet already fully means the dog remains calm. No extra is is needed.