Marcus diligentissimus est, quia menda cito corrigit.

Because it agrees with Marcus.

Marcus is masculine, singular, and nominative, so the adjective describing him must also be masculine, singular, and nominative. The masculine nominative singular form of this adjective is diligentissimus.

If the subject were feminine, you would expect diligentissima instead.

It is the superlative form of diligens, meaning diligent, careful, or hard-working.

So diligentissimus literally means most diligent, but in many sentences Latin superlatives are naturally translated as very diligent or extremely diligent if no explicit comparison is being made.

So the form is grammatically superlative, even if the best English translation is not always most.

Est is the third-person singular present form of esse, to be. It means is.

In this sentence, it links the subject Marcus with the description diligentissimus:

Marcus diligentissimus est = Marcus is very diligent / most diligent

This is a very common Latin pattern:

• subject + predicate adjective + est

Because the verb ending already tells you the subject.

Corrigit means he/she/it corrects, since the ending -it marks third person singular present.

So Latin does not need to say he explicitly here. The subject is understood from the verb, and from the context we know it refers to Marcus.

Corrigit is:

• present tense
• active voice
• indicative mood
• third person singular

It comes from corrigere, meaning to correct.

So corrigit means he corrects or she corrects. In this sentence, it means he corrects, referring to Marcus.

Because menda is a neuter plural form.

The singular is mendum, meaning mistake or fault. Its plural is menda.

This is a very important Latin pattern: for many neuter nouns, the nominative plural and accusative plural end in -a.

Here, menda is the accusative plural, the direct object of corrigit:

• corrigit menda = corrects mistakes

Cito is an adverb, and it means quickly.

It modifies the verb corrigit, telling you how Marcus corrects the mistakes:

• menda cito corrigit = he corrects mistakes quickly

A common thing for English speakers to notice is that Latin often forms adverbs differently from English, and their position in the sentence can be fairly flexible.

Quia means because.

It introduces a reason:

• Marcus diligentissimus est = main statement
• quia menda cito corrigit = reason why that statement is true

So the sentence structure is:

• Marcus is very diligent
• because he corrects mistakes quickly

Latin word order is much more flexible than English word order because Latin uses endings to show grammatical relationships.

English depends heavily on word order:

• He corrects mistakes

Latin can move the words around more freely because:

• corrigit shows the subject is third person singular
• menda shows the object by its form
• cito is clearly an adverb

So menda cito corrigit still means he corrects mistakes quickly, even though it is not in the most English-like order.

Yes.

Marcus diligentissimus est and Marcus est diligentissimus mean the same thing. Latin often places est later in the clause, but it does not have to.

Different word orders can create slightly different emphasis, but the basic meaning stays the same.

Yes.

Marcus is the subject of the sentence, so it is in the nominative case. That is also why diligentissimus is nominative: the adjective agrees with the noun it describes.

So in the first clause:

• Marcus = nominative subject
• diligentissimus = nominative adjective agreeing with Marcus
• est = is

Not necessarily.

A Latin superlative form can sometimes make an actual comparison, as in the most diligent student, but it can also simply intensify the adjective and mean very diligent.

In this sentence, since no comparison group is mentioned, many learners and translators will understand it as very diligent rather than literally the most diligent.