Si ventus saevior erit, scintillae e foco exire poterunt.

Because Latin often uses the future indicative in both parts of a future condition.

So:

• si ventus saevior erit = if the wind is / will be fiercer
• scintillae ... poterunt = the sparks will be able to ...

In English, we usually say if the wind is stronger, the sparks will..., with a present tense in the if-clause. Latin does not have to follow that pattern. A future idea can be shown with future tense in both clauses.

This is completely normal Latin.

This is a future more vivid condition, or more simply a future condition.

The structure is:

• si
  • future indicative
• main clause with future indicative

So the sentence means something like:

• If the wind becomes fiercer, sparks will be able to come out of the hearth.

It presents a real possible future situation, not a hypothetical or contrary-to-fact one.

Saevior is the comparative form of saevus.

Basic idea:

• saevus = fierce, savage, violent
• saevior = fiercer, more violent

With ventus, the sense is something like:

• a fiercer wind
• a stronger / more violent wind

Latin comparatives do not always need an explicit than... phrase. Here saevior can mean fiercer than before, fiercer than usual, or simply rather fierce / more violent in context.

Because Latin does not need quam unless the second thing being compared is stated explicitly.

For example:

• ventus saevior erit = the wind will be fiercer
• ventus saevior quam ante erit = the wind will be fiercer than before

In your sentence, there is no stated second term of comparison, so quam is unnecessary.

Ventus is nominative singular.

You can tell because it is the subject of erit:

• ventus ... erit = the wind will be...

Also, saevior agrees with it:

• masculine
• singular
• nominative

So ventus saevior means the fiercer wind or more naturally the wind, fiercer / becoming fiercer.

Here scintillae is nominative plural, meaning sparks.

Why not singular?

Because the verb poterunt is third person plural:

• poterunt = they will be able

So scintillae must be the plural subject:

• scintillae ... poterunt = the sparks will be able...

It is true that scintillae could also be genitive singular or dative singular in some contexts, but not here. The verb makes the function clear.

Because e or ex is a preposition that takes the ablative.

So:

• e/ex = out of, from
• foco = ablative singular of focus

Together:

• e foco = out of the hearth or from the fireplace/fire

This is a standard Latin construction: motion out from something is often expressed with e/ex + ablative.

Both e and ex mean the same thing here: out of, from.

A common tendency is:

• e before consonants
• ex before vowels and sometimes h

So e foco is very natural because foco begins with a consonant.

That said, Latin authors are not always mechanically strict about this, and both forms can occur. But for a learner, e foco before f is exactly what you would expect.

Yes. Exire is a compound of:

• ex = out
• ire = to go

So exire means:

• to go out
• to come out
• to emerge

With scintillae, a very natural English sense is:

• sparks come out
• sparks fly out

Latin uses the simple verb to go out/come out, while English often prefers a more vivid verb like fly out for sparks.

Because it depends on poterunt, the future of possum.

Possum means to be able, and it normally takes a complementary infinitive:

• possum exire = I am able to go out
• poterunt exire = they will be able to go out

So in this sentence:

• scintillae e foco exire poterunt = the sparks will be able to come out of the hearth

Grammatically, poterunt is the future tense of possum:

• possunt = they are able / can
• poterunt = they will be able / can in the future

In context, English may translate it in different natural ways:

• the sparks will be able to come out
• the sparks can come out
• the sparks may fly out

The Latin specifically marks the situation as future, but idiomatic English may smooth that into can or may, depending on context.

The word order is natural, but Latin word order is much freer than English word order.

The sentence begins with the condition:

• Si ventus saevior erit = If the wind is fiercer...

Then comes the result:

• scintillae e foco exire poterunt = the sparks will be able to come out of the hearth

Because Latin shows grammatical roles through endings, the words could be rearranged without destroying the sense. But this order is clear and straightforward:

1. condition first
2. subject of the main clause
3. phrase of motion
4. infinitive + finite verb

Yes, literally exire means to go out / come out, but English often uses a more specific verb when talking about sparks.

So although the Latin is simple, a natural English rendering might be:

• sparks can fly out of the hearth
• sparks may shoot out from the fire

That is a translation choice, not a difference in grammar. Latin is using its ordinary verb for movement out from somewhere.

Because Latin has no definite article like English the.

So:

• ventus can mean wind or the wind
• scintillae can mean sparks or the sparks
• focus can mean hearth, the hearth, or fireplace, depending on context

Latin leaves that to context. English usually has to choose whether to say the wind, the sparks, and the hearth.