Cum hospes in ātrium intrat, canis in līmine sedet.

Here cum is a conjunction, not the preposition meaning with.

It means when or whenever:

• Cum hospes in ātrium intrat = When the guest enters the atrium...

Latin cum can have different meanings depending on how it is used:

• cum + ablative noun = with
  • for example, cum amīcō = with a friend
• cum + verb clause = when, since, although, etc., depending on context

In this sentence, because cum is followed by a full clause with a verb (intrat), it means when.

Intrat is present tense, third person singular: he/she/it enters.

Latin present tense can cover several ideas that English separates more clearly:

• enters
• is entering
• sometimes, in a more general sense, whenever ... enters

So this sentence can sound like:

• When the guest enters the atrium, the dog sits on the threshold
• or more naturally in English, When the guest is entering the atrium, the dog is sitting on the threshold
• or as a general repeated action, Whenever a guest enters the atrium, the dog sits on the threshold

The exact nuance depends on context, but the Latin form itself is straightforwardly present.

This is one of the most important Latin patterns:

• in + accusative = into / onto a place, showing motion toward
• in + ablative = in / on a place, showing location

So:

• in ātrium: into the atrium
  • ātrium is accusative
  • because the guest is moving into it
• in līmine: on the threshold or at the threshold
  • līmine is ablative
  • because the dog is located there, not moving into it

This contrast is extremely common in Latin.

Here is the case of each noun:

• hospes — nominative singular
  • subject of intrat
• ātrium — accusative singular
  • object of the preposition in with motion
• canis — nominative singular
  • subject of sedet
• līmine — ablative singular
  • object of the preposition in with location

So the structure is:

• Cum hospes in ātrium intrat
  = When the guest enters the atrium
• canis in līmine sedet
  = the dog sits on the threshold

In Latin, you often identify the subject not by position, but by case and verb ending.

In this sentence:

• hospes is nominative, so it is the subject of intrat
• canis is nominative, so it is the subject of sedet

The verbs also help:

• intrat = he/she/it enters
• sedet = he/she/it sits

Because both nouns are nominative singular, each naturally goes with its nearby verb.

English relies heavily on word order. Latin relies much more on endings.

Latin has no articles.

That means Latin does not have separate words for:

• the
• a / an

So:

• hospes can mean guest, a guest, or the guest
• canis can mean dog, a dog, or the dog

You decide from context which English article makes the most sense.

In a simple sentence like this, English usually supplies one naturally:

• When the guest enters the atrium, the dog sits on the threshold

But Latin itself does not explicitly say the.

Yes. Hospes can mean guest, but it can also mean host or even stranger/visitor, depending on context.

That may feel confusing at first, but many Latin words cover a wider range than a single English word.

In this sentence, guest is the most natural meaning:

• Cum hospes in ātrium intrat...
  = When the guest enters the atrium...

If the broader context were different, hospes might be translated another way.

Because this is a simple temporal use of cum: when.

The verb after cum is:

• intrat — present indicative

That is normal when cum simply tells when something happens.

Learners often meet other kinds of cum clauses where Latin uses the subjunctive, especially for ideas like:

• since
• although
• background circumstance

But here there is no special nuance like that. It is just a straightforward when clause, so the indicative makes sense.

Because English and Latin do not always use prepositions in exactly the same way.

Latin says:

• in līmine

Literally, that is something like in/on the threshold, but natural English prefers:

• on the threshold
• at the threshold

So the Latin preposition in with the ablative can sometimes correspond to several English choices, depending on what sounds natural.

The key grammatical point is that līmine is a location, not a destination.

Yes. Latin word order is much more flexible than English word order because the endings show the grammar.

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

• Canis in līmine sedet, cum hospes in ātrium intrat.
• Cum in ātrium hospes intrat, canis in līmine sedet.

However, word order still matters for emphasis and style.

The given order is very natural:

1. the when clause comes first
2. then the main clause follows

So it reads smoothly as:

• When the guest enters the atrium, the dog sits on the threshold

The main dictionary forms are:

• cum — conjunction meaning when
• hospes, hospitis — guest / host / visitor
• in — preposition taking either accusative or ablative depending on meaning
• ātrium, ātriī — atrium, central hall of a Roman house
• intrō, intrāre, intrāvī, intrātum — enter
• canis, canis — dog
• līmen, līminis — threshold
• sedeō, sedēre, sēdī, sessum — sit

This is useful because some forms in the sentence are not the exact dictionary form:

• līmine comes from līmen
• intrat comes from intrō
• sedet comes from sedeō

They are called macrons. They show that the vowel is long:

• ā in ātrium
• ī in līmine

Macrons are very helpful for learners because they show vowel length, which can matter for:

• pronunciation
• meter in poetry
• sometimes distinguishing forms

In many real Latin texts, macrons are not written, but in learning materials they are often included.