Soror rosam rubram et violam albam in aquā pōnit, quia odor eārum suāvis est.

Because they are both direct objects of pōnit.

The verb pōnit means puts/places, so we ask: puts what?
Answer: rosam rubram and violam albam.

In Latin, a direct object is usually put in the accusative case. Since rosa and viola are first-declension nouns, their accusative singular ends in -am:

• rosa → rosam
• viola → violam

The adjectives also match:

• rubra → rubram
• alba → albam

So the endings show that these are the things being placed.

Because Latin adjectives agree with the nouns they describe in gender, number, and case.

Here:

• rosam is feminine singular accusative, so rubram must also be feminine singular accusative
• violam is feminine singular accusative, so albam must also be feminine singular accusative

This agreement is one of the most important features of Latin grammar. Even if the word order changes, the matching endings help you see which adjective goes with which noun.

This is a very common question, because learners are often taught:

• in + accusative = into
• in + ablative = in/on

That rule is useful, but with verbs of placing like pōnere, Latin can sometimes use in + ablative to focus on the place where something ends up being placed, not just the motion into it.

So in aquā pōnit can mean that she places the flowers in the water.

A learner should still know that in aquam would be the more straightforward way to stress motion into the water. But in aquā with a verb of placing is possible and understandable.

Aquā is ablative singular.

It is ablative because it comes after the preposition in in the phrase in aquā. In this sentence, in is being used with the ablative.

The noun is:

• nominative: aqua
• ablative: aquā

So the long -ā ending shows the ablative singular.

Eārum means of them or their, and it refers to rosam rubram et violam albam.

More exactly, eārum is:

• genitive plural
• feminine

That makes sense because its antecedents are two feminine nouns:

• rosa
• viola

So odor eārum means their smell or the smell of them.

Because it refers back to two feminine nouns:

• rosam
• violam

In Latin, pronouns must agree with the nouns they refer to in gender and number. Since there are two flowers, it must be plural. Since both nouns are feminine, it must be feminine.

That is why Latin uses eārum, not eōrum.

Because Latin can speak of the combined fragrance of both flowers as a single thing.

So odor eārum means their scent as one shared smell, not necessarily two separate smells.

English does the same kind of thing:

• their smell is pleasant

even if more than one thing is involved.

If Latin wanted to emphasize separate smells, it could use a plural such as odōrēs, but the singular here is perfectly natural.

Because suāvis is agreeing with odor, which is a masculine singular noun.

The adjective suāvis, suāve is a third-declension adjective:

• suāvis = masculine or feminine singular nominative
• suāve = neuter singular nominative

Since odor is masculine, Latin uses suāvis.

So:

• odor suāvis est = correct
• odor suāve est = not correct

It is a clause introduced by quia, meaning because.

The structure is:

• quia = because
• odor = subject
• eārum = dependent genitive, of them / their
• suāvis = predicate adjective
• est = is

So grammatically it works like:

• because [their smell] [is pleasant]

It is a very standard way to build a reason clause in Latin.

Because the subject is soror, which is singular.

• soror = sister
• pōnit = she puts / the sister puts

Even though there are two objects being placed, the person doing the action is only one person, so the verb is singular.

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

For example, Latin could rearrange parts of this sentence without changing the basic meaning, such as:

• Soror in aquā rosam rubram et violam albam pōnit
• Rosam rubram et violam albam soror in aquā pōnit
• Quia suāvis est odor eārum, soror rosam rubram et violam albam in aquā pōnit

The actual order in your sentence is natural and clear, but not the only possible one.

Because eārum is in the genitive case, and one of the main uses of the genitive is to show possession or association.

So:

• odor eārum = their smell
• literally, the smell of them

This is a very common Latin pattern:

• liber puerī = the boy’s book
• color rosae = the color of the rose
• odor eārum = their smell

A learner would usually look them up like this:

• soror, sorōris = sister
• rosa, rosae = rose
• ruber, rubra, rubrum = red
• viola, violae = violet
• albus, alba, album = white
• aqua, aquae = water
• pōnō, pōnere, posuī, positum = put, place
• quia = because
• odor, odōris = smell, scent
• is, ea, id → eārum comes from this pronoun
• suāvis, suāve = sweet, pleasant

Knowing the dictionary forms helps you see why the sentence forms look the way they do.

The macrons show vowel length:

• aquā
• pōnit
• eārum
• suāvis

They are not usually written in most ancient manuscripts, but modern textbooks often include them to help learners with:

• pronunciation
• meter in poetry
• distinguishing forms

For example, aquā has a long final -ā, which helps show that it is ablative singular. Macrons are very useful for students, even though many printed Latin texts omit them.