Mercator horreum ingreditur et custodem salutat.

Because mercator is in the nominative singular, which is the case normally used for the subject of a finite verb in Latin.

Here, mercator means the merchant or simply merchant, and it is the person doing both actions:

• ingreditur = enters
• salutat = greets

So mercator is the one who enters the warehouse and greets the guard.

Horreum is accusative singular.

It is the direct object of ingreditur. This often surprises English speakers, because in English we usually say enters the warehouse, but with many motion verbs we expect a preposition such as into. In Latin, however, ingredior can take a direct object in the accusative without a preposition.

So:

• horreum ingreditur = he enters the warehouse

You do not need in here.

Because ingreditur is a deponent verb.

A deponent verb:

• has passive-looking forms
• but an active meaning

So although ingreditur looks passive because of -tur, it means he enters, not he is entered.

This is very common in Latin. The dictionary form is usually:

• ingredior, ingredi, ingressus sum = enter

So ingreditur is a normal present-tense form of a deponent verb.

Because salutat comes from a regular active verb, while ingreditur comes from a deponent verb.

Compare them:

• ingreditur = from ingredior

  • deponent
  • passive in form, active in meaning

• salutat = from saluto

  • ordinary active verb
  • active in both form and meaning

So both verbs are active in meaning, but they belong to different verb types.

Custodem is accusative singular.

You can tell because:

• it is the person being greeted
• it is the direct object of salutat

So:

• mercator = subject, nominative
• custodem = object, accusative

This is also a useful example of a third-declension noun:

• nominative singular: custos
• accusative singular: custodem

Because the accusative case is used for more than one function.

In this sentence:

• horreum is accusative because it is the direct object of ingreditur
• custodem is accusative because it is the direct object of salutat

So the accusative does not always mean the same thing in English. It mainly marks what the verb directly affects. With enter, that can be a place. With greet, that can be a person.

Both are in the present tense.

• ingreditur = enters / is entering
• salutat = greets / is greeting

In simple narrative Latin, the present can often be translated in more than one natural way in English, depending on context:

• The merchant enters the warehouse and greets the guard.
• The merchant is entering the warehouse and greeting the guard.

Usually the simple present is the most straightforward translation here.

No. Latin has no definite article like English the.

So:

• mercator can mean merchant or the merchant
• horreum can mean warehouse or the warehouse
• custodem can mean guard or the guard

The context tells you whether English should use the, a, or no article at all.

Yes, Latin word order is more flexible than English word order because the endings show the grammatical roles.

This sentence is perfectly natural as written:

• Mercator horreum ingreditur et custodem salutat

But Latin could rearrange it for emphasis, for example:

• Horreum mercator ingreditur et custodem salutat
• Mercator ingreditur horreum et custodem salutat

The endings still show:

• mercator = subject
• horreum = object of ingreditur
• custodem = object of salutat

Even so, not every order is equally natural in every context. Latin word order often reflects emphasis, style, or rhythm.

A learner often wants to identify the base forms. They are:

• mercator → mercator, mercatoris = merchant
• horreum → horreum, horrei = warehouse, storeroom, granary
• ingreditur → ingredior, ingredi, ingressus sum = enter
• custodem → custos, custodis = guard, keeper
• salutat → saluto, salutare = greet

Knowing the dictionary form helps you understand:

• declension
• conjugation
• irregularities such as deponent verbs

No, et is simply the normal Latin word for and.

It joins the two actions:

• ingreditur
• salutat

So the sentence gives a sequence of actions by the same subject:

• the merchant enters the warehouse
• and greets the guard

Latin et is very common and usually works just like English and.