Si odor lilii et rosae tam suavis est, cur hospes in peristylio non maneat?

Because it depends on odor.

In Latin, odor can take a genitive to show what the smell is of. So:

• odor lilii = the scent of the lily
• odor rosae = the scent of the rose

Together, odor lilii et rosae means the scent of the lily and the rose.

This is similar to English of-phrases, but Latin often uses the genitive instead of a separate word like of.

Because the sentence is talking about the lily and the rose as kinds of flowers, not necessarily many lilies and many roses.

So:

• lilii = of the lily
• rosae = of the rose

Latin often uses the singular in this kind of general statement. English may also do something similar: the scent of the lily and the rose.

If the sentence wanted to emphasize many flowers, it could use plurals instead.

Because suavis describes odor, not lilii et rosae.

The main noun is:

• odor = scent, singular

So the adjective agrees with odor, not with the flowers named in the genitive. That is why we get:

• odor ... suavis est = the scent ... is sweet

Even though two flowers are mentioned, there is still only one scent being spoken of grammatically.

Tam is an adverb meaning so.

It modifies the adjective suavis:

• tam suavis = so sweet

This is a very common Latin pattern:

• tam
  • adjective/adverb = so ...

In this sentence, it sets up the reasoning of the question: If the scent is so sweet, why ... ?

Si means if and introduces a conditional clause.

So the first part of the sentence is:

• Si odor lilii et rosae tam suavis est = If the scent of the lily and the rose is so sweet

This gives the condition or assumption, and the second part asks what follows from it:

• cur hospes in peristylio non maneat? = why does the guest not remain in the peristyle?

This is one of the most important grammar points in the sentence.

• est is indicative because the if-clause states a straightforward condition:
  If the scent ... is so sweet
• maneat is subjunctive because cur can introduce a question of the type why should...? or why would...?

So cur hospes ... non maneat? is not just a plain factual question. It has a more reflective or slightly rhetorical force:

• Why should the guest not stay in the peristyle?
• or more naturally in English, Why doesn't the guest stay in the peristyle?

This is a common use of the subjunctive in Latin questions after words like cur.

It is best understood as a rhetorical or deliberative-style question.

Latin often uses the present subjunctive in questions to suggest:

• why should ... ?
• what is the reason for ... ?
• why would ... ?

So the speaker is not just asking for information. The sentence implies surprise:

If the scent is so sweet, why should the guest not stay there?

In smoother English, this often becomes simply:

If the scent is so sweet, why doesn't the guest stay in the peristyle?

Because hospes is the subject of maneat.

• hospes = guest
• maneat = may stay / should stay / stays depending on context

So hospes must be nominative singular:

• cur hospes ... maneat? = why should the guest stay / why does the guest stay?

Peristylio is ablative because in with the ablative means in or inside a place.

So:

• in peristylio = in the peristyle

This is a location phrase, not motion toward a place.

Compare:

• in peristylio = in the peristyle / inside the peristyle
• in peristylium = into the peristyle

Here the guest is staying in a place, so the ablative is the correct case.

A peristylium is a peristyle: a colonnaded courtyard or open space in a Roman house, usually surrounded by columns.

For a learner, the important point is that it is a part of a house or building, so in peristylio means the guest is remaining in that area of the house.

Because non normally negates the verb.

So:

• maneat = may stay / stays
• non maneat = may not stay / does not stay

Latin word order is flexible, but placing non before the verb is very common and clear.

Not especially, but it is more flexible than English word order.

Latin can arrange words for emphasis as well as grammar. Here the order is quite natural:

• Si odor lilii et rosae tam suavis est
• cur hospes in peristylio non maneat?

A few things to notice:

• odor comes early because it is the subject of the first clause
• lilii et rosae follows it to explain what kind of scent it is
• tam suavis comes before est, a common placement
• in peristylio appears before the verb maneat, which is also common

English depends much more on word order for grammar; Latin depends more on endings.

Yes. Hospes can mean guest, host, or even stranger, depending on context.

In this sentence, guest is the most natural meaning. The context of staying in a part of a house fits that well.

This is a good reminder that Latin words do not always match exactly one English word.

It is a simple or open condition, not a contrary-to-fact one.

The clause uses:

• si
  • present indicative (est)

That usually means the speaker presents the condition as possible or assumed for the sake of argument:

• If the scent is so sweet ...

A contrary-to-fact condition would use subjunctives in a different pattern, such as something like si ... esset.

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

So:

• odor can mean a scent or the scent
• hospes can mean a guest or the guest

You determine the best English wording from context. In this sentence, English naturally uses the:

• the scent of the lily and the rose
• the guest
• the peristyle

It has two parts:

1. Conditional clause
   Si odor lilii et rosae tam suavis est
   = If the scent of the lily and the rose is so sweet

2. Main question
   cur hospes in peristylio non maneat?
   = why does the guest not stay in the peristyle?

So the overall shape is:

If X is true, why Y?

That makes the sentence feel logical and slightly rhetorical at the same time.