Modo sors lusori favet, modo adversario favet.

In this sentence, modo ... modo shows alternation: now ... now, at one time ... at another, or more naturally in English, sometimes ... sometimes.

So the idea is that fortune does not stay on one side; it shifts back and forth.

It is important not to take modo here as only or just now. Because it appears twice, it forms a set expression.

Because favere does not take a direct object in Latin. It takes the dative case.

So:

• lusori = to the player
• adversario = to the opponent

A native English speaker often expects favor someone, with a direct object. Latin instead thinks in terms of show favor to someone.

Both are dative singular.

• lusori comes from lusor, lusoris = player
• adversario comes from adversarius, adversarii = opponent/adversary

They are in the dative because of the verb favet.

Favet is:

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

It comes from faveo, favere = to favor.

So favet means he/she/it favors.
Here the subject is sors, so it means fortune/chance favors.

Because the subject is sors, which is singular.

• sors = lot, fate, fortune, chance
• It is a singular noun
• Therefore the verb must also be singular: favet

Even though there are two people involved, they are not the subject. They are the ones receiving favor, so they are in the dative.

Sors is nominative singular, because it is the subject of the verb.

In other words, sors is the thing doing the favoring:

• sors favet = fortune favors

This noun belongs to the third declension:

• nominative: sors
• genitive: sortis

Yes, but only something that Latin can easily leave understood.

The full idea is:

• modo sors lusori favet
• modo sors adversario favet

In the second clause, sors is omitted because it is already obvious from the first clause. Latin often leaves out repeated words when the meaning is clear.

So the second half still means now fortune favors the opponent.

Latin word order is more flexible than English because the endings show each word’s job in the sentence.

A very literal arrangement here is:

• modo = now / sometimes
• sors = fortune
• lusori = to the player
• favet = favors

English usually wants a more fixed order, but Latin can move words around for rhythm, emphasis, or style.

Here the repeated modo at the beginning of each clause nicely highlights the back-and-forth pattern.

The word adversarius can be either:

• an adjective, meaning opposed or hostile
• or a noun, meaning opponent/adversary

Here it is being used as a noun: adversario = to the opponent.

This is very common in Latin. An adjective can become a noun when the context makes the person or thing clear.

Because the repeated modo ... modo already links the two parts strongly enough.

It creates a balanced pattern by itself:

• modo ...
• modo ...

That pattern expresses contrast and alternation, so no extra connecting word is necessary.

It consists of two parallel clauses:

• modo sors lusori favet
• modo adversario favet

More fully, the second clause is understood as:

• modo sors adversario favet

So the structure is:

• modo
  • subject + dative + verb
• modo
  • understood subject + dative + verb

This parallelism is one of the reasons the sentence sounds neat and balanced in Latin.