Convīva mātrī grātiās agit, quod epulae simplicēs sed bonae sunt.

Convīva means guest, dinner guest, or banquet guest. Here it is nominative singular, so it is the subject of agit.

So the basic subject-verb idea is:

Convīva agit = The guest gives / does

In this sentence, that becomes the idiomatic gives thanks.

Mātrī is the dative singular of māter.

In Latin, the person to whom thanks are given is often put in the dative with the expression grātiās agere. So:

• māter = mother as a subject
• mātrī = to the mother / for the mother

Even though English usually says the guest thanks the mother, Latin uses the idiom give thanks to the mother.

Grātiās agere is a very common Latin idiom meaning to give thanks or simply to thank.

Literally:

• grātiās = thanks
• agit = does / drives / gives, depending on context

But together, grātiās agit means he/she gives thanks.

So you should learn it as a set expression:

alicuī grātiās agere = to thank someone

In this expression, Latin normally uses grātiās in the accusative plural.

So although English often uses singular-looking thanks as a fixed word, Latin also uses a fixed plural form here:

grātiās agere = to give thanks

This is just the standard idiom. Learners usually do best by memorizing the whole phrase rather than trying to translate each part too mechanically every time.

Agit is:

• 3rd person singular
• present tense
• active
• indicative

from agō, agere.

Because the subject convīva is singular, the verb is singular too:

• convīva agit = the guest gives thanks

If the subject were plural, you would expect agunt instead.

Here quod means because.

It introduces the reason:

quod epulae simplicēs sed bonae sunt
= because the dishes/meal are simple but good

In other contexts, quod can also mean which or the fact that, but here it is clearly a causal conjunction: because.

Epulae is one of those Latin nouns that is very often used in the plural. It means feast, banquet, or dishes/food.

So even if English might sometimes use a singular idea like the meal, Latin says epulae and treats it as plural:

• epulae sunt = the dishes/meal are

That is why the verb is sunt, not est.

Both adjectives describe epulae, so they must agree with it in:

• gender: feminine
• number: plural
• case: nominative

So:

• epulae = nominative feminine plural
• simplicēs = nominative feminine plural
• bonae = nominative feminine plural

This is standard Latin adjective agreement.

Because epulae is feminine plural.

The adjective bonus, bona, bonum must match the noun it describes. Since epulae is feminine plural, the correct form is:

bonae

If the noun were feminine singular, then bona would be right.

The subject of that clause is epulae, which is plural. Therefore the verb must also be plural:

• epulae sunt = the dishes are

Latin verbs agree with their subjects in number, just as English verbs do.

Sed means but.

It connects the two adjectives:

• simplicēs = simple
• bonae = good

So:

simplicēs sed bonae = simple but good

This gives a mild contrast: the food is not fancy, but it is still good.

It may feel unusual to an English speaker, but it is perfectly normal Latin.

The sentence is arranged as:

• Convīva mātrī grātiās agit = main statement
• quod epulae simplicēs sed bonae sunt = reason

A very literal order would be:

The guest to-the-mother thanks gives, because the dishes simple but good are.

More natural English is:

The guest thanks the mother because the dishes are simple but good.

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

Not naturally in this sentence.

If you say:

Convīva mātrī grātiās agit, quod epulae simplicēs sed bonae sunt

the best meaning is:

The guest thanks the mother because the dishes are simple but good.

Using that in English would sound awkward here. The clause is giving the reason for the thanks, so because is the right translation.