Emptor respondet se unum tantum denarium habere.

Because Latin very often uses an indirect statement after verbs of saying, thinking, knowing, hearing, and similar verbs.

In English, we say:

• The buyer answers that he has only one denarius.

In Latin, instead of that + finite verb, you usually get:

• accusative subject + infinitive

So:

• se = the subject of the reported statement
• habere = the verb of the reported statement

That is why Latin says respondet se ... habere rather than using a separate finite verb like habet.

Se is the reflexive pronoun. It refers back to the subject of the main verb, which here is emptor.

So:

• Emptor respondet = The buyer answers
• se ... habere = that he has ...

Latin uses se because the person doing the answering is the same person as the person who has the denarius.

If it referred to someone else, Latin would use a different pronoun, such as eum.

In a Latin indirect statement, the subject of the reported clause goes into the accusative.

So even though se is logically the subject of habere, it appears in the accusative because that is how the construction works.

You can think of the pattern like this:

• main verb of saying/thinking/etc.
• accusative subject
• infinitive verb

So:

• respondet
• se
• habere

Because in an indirect statement, Latin normally puts the reported verb in the infinitive.

So English:

• he answers that he has

becomes Latin:

• respondet se ... habere

The infinitive here is present infinitive, which usually shows action happening at the same time as the main verb. So the sense is:

• he answers that he has
• not that he had
• not that he will have

Because emptor is the subject of respondet.

• emptor = the buyer
• respondet = answers

The subject of a finite verb is normally in the nominative case, so emptor must be nominative singular.

Because denarium is the direct object of habere, so it must be in the accusative case.

Since unum modifies denarium, it has to agree with it in case, number, and gender:

• denarium = masculine, singular, accusative
• unum = masculine, singular, accusative

So:

• unus denarius = one denarius as a subject
• unum denarium = one denarius as an object

Here it is the object of habere, so unum denarium is correct.

Here tantum means only or just.

So:

• unum denarium = one denarius
• unum tantum denarium = only one denarius

In this sentence, tantum is being used adverbially, adding the idea of limitation. It does not mean so great here; it means only.

Because they do different jobs.

• unum gives the number: one
• tantum adds the restriction: only

So unum tantum denarium is stronger than just unum denarium.

Compare:

• unum denarium habet = he has one denarius
• unum tantum denarium habet = he has only one denarius

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

This sentence is arranged in a very natural Latin way:

• Emptor — subject first
• respondet — main verb
• se ... habere — indirect statement
• habere at the end — a common place for the infinitive or verb

The order also lets unum tantum denarium stand out near the end, which helps emphasize the small amount of money.

Other word orders would be possible, but they might shift the emphasis slightly.

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

English says:

• The buyer answers that he has only one denarius.

Latin normally expresses this with the accusative-and-infinitive construction instead:

• Emptor respondet se unum tantum denarium habere.

So the idea of that is built into the construction itself, rather than being expressed by a separate word.

Not necessarily.

Grammatically, se is reflexive, so it does mean himself/herself/themselves depending on context. But in English, a literal translation may sound awkward.

So although se is reflexive in Latin, the best English translation is often just:

• he

rather than:

• himself

In other words, you should understand the grammar of se, but you do not always need to force himself into the English translation.