Mercator respondet oleum quoque carum constare, quia annus difficilis fuit.

Because after a verb like respondet in this sentence, Latin is using indirect statement.

Instead of saying:

• the merchant answers that oil is expensive

Latin often says:

• the merchant answers oil to be expensive

That is why you get:

• respondet ... constare

Here constare is the infinitive, and the whole phrase oleum quoque carum constare is what the merchant is saying in reply.

This is a very common Latin pattern:

• verb of saying/thinking/perceiving
• accusative + infinitive

So the sentence structure is:

• Mercator respondet = the merchant replies
• oleum quoque carum constare = that oil also is expensive / that oil too costs a lot

Normally, yes: the subject of a verb is usually nominative.

But in an accusative-and-infinitive construction, the subject of the infinitive goes into the accusative.

So in:

• oleum quoque carum constare

oleum is the logical subject of constare, but because constare is an infinitive inside indirect statement, oleum becomes accusative.

You can think of it like this:

• main subject: mercator
• main verb: respondet
• subject of the infinitive: oleum (in accusative because of the construction)

Constare can mean to cost.
With carum, it means to cost dearly, or more naturally in English, to be expensive.

So:

• oleum carum constat = oil is expensive / oil costs a lot
• oleum carum constare = oil to be expensive / that oil is expensive

A learner might expect an actual price, such as decem denarios constat = it costs ten denarii. But Latin can also use constare more generally with carus to express high cost.

Here carum agrees with oleum:

• oleum = neuter singular accusative
• carum = neuter singular accusative

So carum is a predicate adjective: oil to be expensive.

Quoque means also or too.

In Latin, quoque usually comes after the word it especially emphasizes.

So:

• oleum quoque = oil too / oil also

That suggests that something else has already been mentioned as expensive, and now the merchant adds that oil is expensive as well.

This position is very normal for quoque. A native English speaker may want to put also before the word, but Latin often puts quoque after it.

It literally means answers, replies, or responds.

Form:

• respondet
• 3rd person singular
• present active indicative
• from respondere

In context, English might translate it as:

• the merchant replies
• the merchant answers
• sometimes even the merchant says in reply

So the basic idea is that the merchant is giving an answer, and what follows is the content of that answer.

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

English:

• the merchant replies that oil is expensive

Latin:

• mercator respondet oleum carum constare

Latin expresses that-clause meaning by using the accusative + infinitive instead.

So the idea of that is there in the grammar, even though there is no separate word for it.

Quia means because and introduces a subordinate clause giving the reason.

So:

• quia = because
• annus = year
• difficilis = difficult
• fuit = was / has been

This clause explains why oil is expensive.

A native English speaker might wonder whether quia always takes the indicative. Very often it does, especially when the cause is presented as a fact. Here annus difficilis fuit is presented as a real reason: the year was difficult.

That is a very good question, because both can often be translated as was, but they are not exactly the same.

• fuit is perfect tense
• erat is imperfect tense

Here fuit presents the difficult year as a completed fact:

• the year turned out to be difficult
• there was a difficult year

If Latin used erat, it would sound more like background description:

• the year was difficult
• it was being difficult / was in a state of being difficult

In many contexts both could make sense, but fuit here neatly states the reason as a finished fact.

Latin word order is much more flexible than English word order, because Latin relies heavily on endings to show grammatical relationships.

English depends strongly on order:

• the merchant replies that oil is also expensive

Latin can arrange words more freely:

• Mercator respondet oleum quoque carum constare, quia annus difficilis fuit.

This order does a few useful things:

• Mercator respondet puts the speaker first
• oleum quoque keeps quoque attached to what it emphasizes
• quia annus difficilis fuit leaves the reason until the end

So the order is not random; it is flexible but meaningful.

Because Latin has no articles.

So:

• mercator can mean the merchant or a merchant
• annus can mean the year or a year

The context tells you which is more natural in English.

That means when reading Latin, you often have to supply the or a when translating, even though there is no separate Latin word for it.

Yes. Difficilis is an adjective agreeing with annus.

Forms:

• annus = masculine singular nominative
• difficilis = masculine/feminine singular nominative

So annus difficilis means a difficult year or the difficult year.

A learner may notice that difficilis does not look like a typical first/second-declension adjective such as bonus, bona, bonum. That is because difficilis is a third-declension adjective. Even so, it still agrees with the noun in gender, number, and case.

Yes. Constare has several meanings in Latin depending on context, such as:

• to stand together
• to be established
• to be certain
• to cost

Here the context clearly points to to cost / to be expensive, especially because of carum and the explanatory clause about a difficult year.

So vocabulary in Latin often depends heavily on context, and constare is a good example of that.