Pater dicit se post laborem in sella quiescere velle, dum mater de hospite cogitat.

Se is the reflexive pronoun, and in this sentence it refers back to the subject of dicit, namely pater.

So Pater dicit se ... velle means Father says that he wants ..., where he = father.

A learner often expects eum, but eum would normally refer to some other male person, not back to the subject of the main clause. Latin uses se when the person inside the reported statement is the same as the subject of the reporting verb.

Because Latin often expresses reported speech with an accusative-and-infinitive construction.

After a verb like dicit (says), the subject of the reported statement does not stay in the nominative. Instead, it goes into the accusative, and the verb of that reported statement becomes an infinitive.

So:

• pater dicit = father says
• se ... velle = that he wants ...

That is why se, even though it is the logical subject of velle, appears in the accusative.

They do two different jobs.

• velle is infinitive because it is the verb of the reported statement after dicit
• quiescere is infinitive because it depends on velle: to want to rest

So the structure is basically:

• pater dicit
• se velle
• quiescere

In smoother English: Father says that he wants to rest.

So velle belongs to the indirect statement, while quiescere is the complementary infinitive that completes the meaning of velle.

Because classical Latin usually does not use a separate word like English that in this kind of sentence.

English says:

• Father says that he wants to rest

Latin more often says:

• Father says himself to want to rest

That sounds strange in English, but it is the normal Latin pattern. The combination of accusative subject + infinitive does the job that English that does.

Because post is a preposition that takes the accusative.

So:

• post = after
• laborem = accusative of labor

This is not the direct object of a verb. It is simply the object of the preposition post.

Because in takes different cases depending on whether there is location or motion toward something.

• in + ablative = in/on a place, with no movement
• in + accusative = into/onto a place, with movement toward it

Here the father wants to rest already seated there, so Latin uses in sella with the ablative.

If the idea were to sit down onto the chair, then a form with motion might be used instead.

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

With seats, Latin often uses in where English prefers on. So in sella can naturally mean on the chair or in the chair, depending on context and idiom.

A very literal translation of prepositions is often misleading. It is better to learn the whole phrase as a normal Latin way of expressing location with a seat.

De hospite means about the guest or concerning the guest.

The verb cogitare is often used with de + ablative when the meaning is to think about someone or something.

So:

• de = about, concerning
• hospite = ablative of hospes

That is why Latin says mater de hospite cogitat for the mother is thinking about the guest.

Here dum means while.

It introduces a clause happening at the same time as the main action:

• Pater dicit ...
• dum mater de hospite cogitat

So the sense is: Father says this while mother is thinking about the guest.

In other contexts, dum can also mean as long as or until, but here the meaning is clearly while.

Because this is a straightforward temporal clause: while mother is thinking about the guest.

Latin commonly uses dum + present indicative for an action going on at the same time as the main action. There is no special idea here such as purpose, fear, doubt, or result that would call for the subjunctive.

So dum mater de hospite cogitat is a normal temporal clause with the indicative.

To an English speaker, yes, it may feel unusual. In Latin, however, word order is much more flexible.

Placing velle at the end is very natural, because it neatly closes the indirect statement:

• se post laborem in sella quiescere velle

Latin often saves an important verb until the end of its clause. The endings on the words show how they fit together, so Latin does not rely on word order as heavily as English does.