Se este não funcionar, eu vou usar o outro.

In this sentence, funcionar is the future subjunctive.

After se when Portuguese is talking about a possible future situation, Portuguese usually uses this pattern:

• Se + future subjunctive, ...
• If + present tense, ... in English

So:

• Se este não funcionar, eu vou usar o outro.
• Literally: If this not work (in the future), I’m going to use the other one.

For regular -ar verbs, the future subjunctive often looks exactly like the infinitive, so funcionar can be confusing.

Compare:

• Se ele vier, eu aviso. = If he comes, I’ll let you know.
• Se eu puder, eu ajudo. = If I can, I’ll help.

Those irregular forms make it easier to see that this is not just the infinitive.

Portuguese and English organize if-clauses differently.

In English, we usually say:

• If this doesn’t work, I’ll use the other one.

Even though the meaning is future, English uses the present tense in the if-clause.

Portuguese normally uses the future subjunctive for that kind of future possibility:

• Se este não funcionar, eu vou usar o outro.

So the tense choice is different, even though the meaning is the same.

Este means this one here.

Traditional Portuguese distinguishes:

• este = this, near the speaker
• esse = that, near the listener or previously mentioned
• aquele = that over there

However, in Brazilian Portuguese, everyday speech often reduces this distinction, and many speakers use esse where grammar books would prefer este.

So:

• Se este não funcionar... = correct
• Se esse não funcionar... = also very common in Brazil

In this sentence, este sounds a bit more careful, specific, or formal.

Because both are being used as pronouns, not adjectives.

They stand in for a noun that is understood from context, such as:

• Se este aparelho não funcionar, eu vou usar o outro aparelho.
• If this device doesn’t work, I’ll use the other device.

Portuguese often does this, just like English says:

• this one
• the other one

So in the original sentence:

• este = this one
• o outro = the other one

Because o outro means the other one, while outro by itself often means another or a different one.

Compare:

• vou usar o outro = I’m going to use the other one
• vou usar outro = I’m going to use another one / a different one

The article o makes it more specific.

In Portuguese, não normally goes directly before the verb it negates.

So:

• não funcionar = not work
• não vou usar = I’m not going to use

In your sentence, the idea is:

• if this one does not work

So não goes before funcionar:

• Se este não funcionar...

Portuguese often allows the subject pronoun to be omitted when it is clear from the verb.

So both are possible:

• eu vou usar o outro
• vou usar o outro

Both mean the same thing here.

Including eu can:

• add emphasis
• make the sentence clearer
• sound a little more explicit

In everyday Brazilian Portuguese, both versions are natural.

Yes.

These are both possible:

• eu vou usar o outro
• usarei o outro

But they do not sound exactly the same in tone.

In Brazilian Portuguese:

• vou usar is more common in everyday speech
• usarei sounds more formal, written, or deliberate

So the original sentence sounds natural and conversational.

The comma separates the if-clause from the main clause.

Structure:

• Se este não funcionar, = if this one doesn’t work
• eu vou usar o outro. = I’m going to use the other one

This is standard punctuation and helps readability.

It can be used more broadly.

It often means:

• to function
• to work
• to operate
• to be effective

So it can refer to:

• a machine: O computador não funciona.
• a plan or method: Essa ideia não funciona.
• a solution: Se isso não funcionar...

In your sentence, it most likely means something like if this one doesn’t work / doesn’t function properly.

Yes, the sentence is correct and natural.

But in everyday Brazilian Portuguese, you might also hear slightly different versions, such as:

• Se esse não funcionar, vou usar o outro.
• Se isso não funcionar, vou usar o outro.

Why the variation?

• esse is very common in speech
• eu is often omitted
• isso may be used if the speaker is referring to a thing or option more generally rather than specifically this one

So the original sentence is perfectly fine, but spoken Brazilian Portuguese often becomes a little simpler.