Avaritia atque luxuria bonos mores laedunt.

Because the sentence has a compound subject: avaritia atque luxuria = greed and luxury.

Each noun by itself is singular, but together they make a plural idea, so the verb must also be plural:

• avaritia laedit = greed harms
• luxuria laedit = luxury harms
• avaritia atque luxuria laedunt = greed and luxury harm

So laedunt is third person plural to match the two subjects taken together.

Here atque simply means and.

So:

• avaritia atque luxuria = greed and luxury

In many sentences, atque and et can both be translated as and. Very often, the difference is more about style or emphasis than basic meaning. Atque can sometimes feel a little stronger or closer-binding than et, rather like and indeed or and also, but in a sentence like this, the simplest translation is just and.

Because bonos mores is the direct object of laedunt, so it must be in the accusative case.

Here is the breakdown:

• mores = accusative plural of mos
• bonos = accusative plural masculine of bonus

The adjective must agree with the noun it modifies in:

• gender
• number
• case

Since mores is masculine accusative plural, the adjective must also be masculine accusative plural: bonos.

If you used boni mores, that would be nominative plural, which would make it the subject, not the object.

Latin often uses mores in the plural to mean customs, conduct, character, or morals.

So boni mores is a very common Latin expression meaning something like:

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

The singular mos usually means custom, habit, or way in an individual sense. But when Latin talks about a person’s or society’s moral behavior, the plural mores is very common.

Laedunt is:

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

It comes from the verb laedo, laedere, laesi, laesum, meaning to harm, injure, damage, or undermine.

So laedunt means:

• they harm
• they damage
• they injure

In this sentence, the they is avaritia atque luxuria.

They are from different declensions:

• avaritia = first declension, nominative singular
• luxuria = first declension, nominative singular
• mos = third declension, with mores here as accusative plural

You can often recognize first-declension nominative singular nouns by the -a ending:

• avaritia
• luxuria

But mos is less obvious because it is a third-declension noun. Its forms include:

• nominative singular: mos
• genitive singular: moris
• accusative plural: mores

So mores is not a nominative here; context and syntax show it is the object of the verb.

Because it agrees with mores, and mos, moris is a masculine noun.

Even though English words like morals or conduct do not have grammatical gender, Latin nouns do. Since mores is masculine plural accusative, the adjective must match it:

• bonos mores = masculine accusative plural

So bonos is masculine not because the idea is masculine in meaning, but because the noun mores is grammatically masculine.

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

In this sentence:

• avaritia atque luxuria = subject
• bonos mores = object
• laedunt = verb

This subject–object–verb order is very natural in Latin, especially in formal or literary style. English depends heavily on position, but Latin does not need to, because:

• -unt on laedunt shows the verb is plural
• bonos mores is clearly accusative
• avaritia and luxuria are nominative

So the sentence can keep the verb until the end without causing confusion.

Yes, Latin could have used other common ways to say and:

• avaritia et luxuria
• avaritia luxuriaque

All three can mean greed and luxury.

The differences are mostly stylistic:

• et = the most straightforward and
• -que = an enclitic, attached to the second word, often linking closely
• atque = also means and, sometimes with a slightly stronger or smoother connective feel

So atque is not required by grammar here; it is just one valid way to join the two nouns.

Because their forms are nominative singular, which is the normal case for the subject.

Meanwhile, bonos mores is accusative, marking it as the direct object.

So the structure is:

• avaritia = nominative subject
• luxuria = nominative subject
• bonos mores = accusative object
• laedunt = plural verb

Even though English relies mostly on word order, Latin relies heavily on case endings. Those endings tell you who is doing the action and who is receiving it.

It can do both.

Laedere often means:

• to injure
• to hurt
• to damage
• to offend
• to harm

In this sentence it is clearly not about physical injury. Greed and luxury are said to harm good morals, so the idea is moral or social damage: they corrupt, weaken, or undermine good conduct.

That broader sense of laedere is very common in Latin.