Lucia menda diligentius quam Marcus corrigit.

• Lucia = the subject, in the nominative case
• menda = the direct object, mistakes
• diligentius = a comparative adverb, more carefully or more diligently
• quam = than
• Marcus = the subject of the comparison clause
• corrigit = corrects

So the structure is basically:

Lucia [corrigit] menda diligentius quam Marcus corrigit

That is, Lucia corrects mistakes more carefully than Marcus does.

Menda is the accusative plural of mendum, a neuter second-declension noun meaning mistake or fault.

For neuter nouns in Latin:

• nominative singular: often -um
• accusative singular: also -um
• nominative plural: -a
• accusative plural: also -a

So:

• mendum = mistake
• menda = mistakes

Even though menda ends in -a, here it is not feminine singular. It is neuter plural, and it works perfectly as the direct object.

Because the sentence is making a comparison.

• diligenter = carefully
• diligentius = more carefully

So diligentius is the comparative form of the adverb. It tells you that Lucia is not just correcting carefully, but more carefully than Marcus.

This is similar to English:

• carefully
• more carefully

Quam introduces the second part of the comparison: than Marcus corrects.

Since diligentius means more carefully, Latin normally uses quam to complete the comparison:

• diligentius quam Marcus corrigit = more carefully than Marcus corrects

So quam connects Lucia's action with Marcus's action and shows that the two are being compared.

It is primarily a comparison between the manner of correcting.

Because diligentius is an adverb, it modifies the verb corrigit. So the meaning is:

• not simply Lucia is more careful than Marcus
• but Lucia corrects more carefully than Marcus corrects

If Latin wanted to compare Lucia and Marcus as people using an adjective, the sentence would be built differently.

Latin often leaves out a word when it is easy to understand from context. Here, the verb is understood with Lucia as well.

So the full idea is:

Lucia menda diligentius corrigit quam Marcus corrigit

And in even fuller English:

Lucia corrects mistakes more carefully than Marcus corrects mistakes.

Latin does not need to repeat everything if the meaning is clear. In this sentence:

• the verb corrigit is expressed once
• the object menda is also understood with Marcus

This kind of omission is very common.

Yes. In the expressed clause after quam, Marcus is the subject of corrigit.

So:

• Marcus corrigit = Marcus corrects

Meanwhile, Lucia is the subject of the understood verb in the first part:

• Lucia [corrigit]

So the sentence compares:

• what Lucia does with
• what Marcus does

Yes. Latin word order is flexible. A learner might find this fuller order easier to understand:

Lucia menda diligentius corrigit quam Marcus.

Or, with everything spelled out:

Lucia menda diligentius corrigit quam Marcus menda corrigit.

These all mean essentially the same thing. The original sentence is normal Latin, but Latin often places the verb later than English does, and it often omits repeated words.

It describes corrigit, not menda.

That is because diligentius is an adverb, and adverbs modify verbs, adjectives, or other adverbs. Here it tells us how the correcting is done:

• corrigit diligentius = corrects more carefully

It does not mean that the mistakes themselves are somehow more careful.

Because each subject is singular:

• Lucia = one person
• Marcus = one person

So the verb is third person singular:

• corrigit = he/she corrects

If the subject were plural, then the verb would be plural as well. But here both people are taken one at a time in the comparison, so singular corrigit is correct.