Lassitudo puellam in cubili manere cogit.

The endings tell you.

• lassitudo is nominative singular, so it is the subject: the thing doing the action.
• puellam is accusative singular, so it is the direct object: the person affected by the action.
• cogit is third person singular, so it matches a singular subject such as lassitudo.

So grammatically, lassitudo is what does the compelling, and puellam is the one compelled.

Because cogere normally takes:

• a direct object = the person being compelled
• an infinitive = the action that person is compelled to do

So the pattern is:

aliquem + infinitive + cogere
= to force someone to do something

Here:

• puellam = the someone
• manere = the action

That is why puellam is accusative.

After cogit from cogere, Latin uses an infinitive to express the action that is being forced.

So:

• cogit = forces / compels
• manere = to remain / to stay

Together, puellam ... manere cogit means forces the girl to remain/stay ...

This is very similar to English force someone to stay, except Latin does not need a separate word exactly like English to in that position; the infinitive form manere already does that job.

cubili is ablative singular, used after in to show location.

So:

• in + ablative = in / on / at a place
• in + accusative = into a place, showing motion toward it

Here there is no motion into somewhere; the idea is staying in a place. So Latin uses:

• in cubili = in bed / on the bed / in the bedchamber, depending on context

If it meant motion into the bed, you would expect in cubile instead.

Latin has no articles like English the or a/an.

So puellam can mean:

• the girl
• a girl

and cubili can mean:

• the bed
• a bed

You decide from context which English article sounds best. That is normal in Latin.

Latin word order is much more flexible than English because the noun endings show each word’s role.

A very common Latin habit is to place the main verb near the end of the sentence, so cogit at the end sounds natural.

The order here also helps the reader unfold the thought step by step:

• Lassitudo — the cause
• puellam — the person affected
• in cubili manere — what she is made to do
• cogit — the final main verb

So the order is natural and stylistically effective, not random.

Often, yes. Because the endings show the grammar, Latin can move words around more freely than English.

For example, these would still express the same basic idea:

• Puellam lassitudo in cubili manere cogit.
• In cubili puellam manere lassitudo cogit.

However, changing the order can change the emphasis.
The original sentence gives prominence to lassitudo at the start and puts cogit in the strong final position.

No. In this sentence cogit is from cogere, meaning to force, compel.

Its dictionary form is:

• cogo, cogere, coegi, coactum

A learner may confuse it with cogitare, which means to think, but that verb gives cogitat, not cogit.

So here cogit definitely means forces / compels, not thinks.

Because lassitudo is a third-declension noun, not a first- or second-declension noun.

Its dictionary form is:

• lassitudo, lassitudinis = weariness, fatigue, tiredness

Third-declension nominative singular forms can have many different endings, including -o. So even though lassitudo ends in -o, it is still nominative singular here.

This is one reason Latin learners must pay attention to declension patterns, not just guess from one ending.

Here are the usual dictionary forms:

• lassitudo, lassitudinis (f.) — weariness, fatigue
• puella, puellae (f.) — girl
• cubile, cubilis (n.) — bed, couch, sleeping-place
• maneo, manere, mansi, mansum — remain, stay
• cogo, cogere, coegi, coactum — force, compel

Knowing these forms helps you see how the sentence is built:

• lassitudo comes from lassitudo
• puellam comes from puella
• cubili comes from cubile
• manere is the infinitive of maneo
• cogit comes from cogo