Discipulus bonus bonos mores semper servare debet.

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

Here, the finite verb is debet (he ought / must), so discipulus is the person who has the obligation.

• discipulus = nominative singular, the student
• debet = ought / must

So discipulus is the one who ought to preserve something.

Because bonus is an adjective describing discipulus, and adjectives in Latin must agree with the nouns they modify in:

• gender
• number
• case

Discipulus is:

• masculine
• singular
• nominative

So the adjective must also be:

• masculine
• singular
• nominative

That gives bonus.

So:

• discipulus bonus = a good student

If it were bonum, that would be masculine accusative singular or neuter nominative/accusative singular, so it would not match discipulus here.

Because bonos modifies mores, and again the adjective must agree with the noun.

Mores is:

• masculine
• plural
• accusative

So the adjective must also be:

• masculine
• plural
• accusative

That gives bonos.

So:

• bonos mores = good morals / good conduct / good manners

In Latin, mos, moris often appears in the plural as mores, especially when referring to:

• morals
• habits
• character
• customs
• manners

So although English might sometimes use a singular idea like good behavior or good character, Latin commonly uses the plural mores.

This is very natural Latin usage, not something unusual in this sentence.

It is accusative plural, because it is the direct object of servare.

The action is to preserve something. What is being preserved?

• bonos mores

So bonos mores is the thing directly affected by the verb, and that puts it in the accusative.

Because debet is followed by an infinitive in Latin, just as English must, ought, or should is followed by a basic verb form.

So the structure is:

• debet servare = ought to preserve / must preserve

Here:

• debet is the finite verb
• servare is the complementary infinitive

This is a very common Latin pattern:

• potest facere = he can do
• vult venire = he wants to come
• debet servare = he ought to preserve

Debet is:

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

from the verb debeo, debere.

It means:

• he/she/it owes
• and very commonly, he/she/it ought to or must

Because the subject is discipulus, we understand:

• the student ought to preserve

Servare is the present active infinitive of servo, servare, meaning to preserve, to keep, or to observe.

So in this sentence:

• servare debet = ought to preserve

It is not a finite verb by itself here; it depends on debet.

Semper is an adverb meaning always. Latin adverbs are often fairly flexible in position.

Here it stands before servare:

• bonos mores semper servare debet

This naturally emphasizes the ongoing nature of the action: the student ought always to preserve good morals.

Latin could place semper in other positions too, for example:

• Discipulus bonus semper bonos mores servare debet
• Discipulus bonus bonos mores servare semper debet

All are possible, though some word orders may sound more natural than others depending on emphasis.

The word order matters more for emphasis and style than for basic grammar, because the endings show the relationships.

From the endings, we can tell that:

• discipulus bonus is the subject
• bonos mores is the object
• servare is the infinitive
• debet is the main verb

So even if the order changed, the core meaning would stay the same as long as the forms stayed the same.

Still, this order is very natural Latin:

• subject first
• object before the verb
• main verb at the end

Latin often likes to place the finite verb near the end of the sentence.

Because the Latin infinitive is a single word, while English usually uses to + verb for the infinitive.

So:

• Latin servare
• English to preserve

The Latin infinitive does not need a separate word corresponding to English to.

The dictionary form is mos, moris.

That tells you:

• nominative singular: mos
• genitive singular: moris

From that stem, the accusative plural is mores.

This can be confusing for English speakers because the noun often appears in the plural in actual sentences, even though the dictionary entry is singular.

Because mos, moris is a third-declension noun.

That is why its accusative plural is mores rather than something like -os or -as.

A useful pattern to remember is that many third-declension masculine and feminine nouns have:

• nominative singular: variable
• genitive singular: -is
• accusative plural: -es

So:

• mos, moris
• accusative plural: mores

It can cover several related ideas, depending on context:

• good morals
• good character
• good conduct
• good manners
• proper behavior

Latin mores is broader than a single neat English word. It often refers to the habits and standards by which a person lives.

So the phrase has a wider sense than just table manners or politeness.

Yes, bonus is a broad adjective meaning good, but the exact shade depends on what it describes.

With discipulus, bonus can mean something like:

• good
• worthy
• well-behaved
• diligent

The sentence does not force only one nuance. It simply describes the student positively.

You can say it contains one finite verb and one infinitive.

• debet = the finite verb, the grammatical center of the sentence
• servare = an infinitive depending on debet

So there are two verbal forms, but only debet is a fully conjugated verb in the sentence.

That distinction is useful in Latin grammar.

A simple parse would be:

• Discipulus — noun, nominative singular masculine, subject
• bonus — adjective, nominative singular masculine, modifying discipulus
• bonos — adjective, accusative plural masculine, modifying mores
• mores — noun, accusative plural masculine, direct object
• semper — adverb, always
• servare — present active infinitive, complement of debet
• debet — 3rd person singular present active indicative, main verb

That is a very good way to break down the sentence when learning Latin.