Breakdown of Se eu gastar muito hoje, não vou economizar para as férias.
eu
I
não
not
hoje
today
ir
to go (future auxiliary)
Questions & Answers about Se eu gastar muito hoje, não vou economizar para as férias.
Why is it Se eu gastar and not Se eu gasto?
Because Portuguese usually uses the future subjunctive after se when talking about a possible future condition.
So:
If you say Se eu gasto, that sounds unnatural in standard Brazilian Portuguese for this meaning.
A very common pattern is:
- Se + future subjunctive, main clause in the future / near future / imperative
Examples:
- Se eu tiver tempo, vou ligar.
- Se chover, ficamos em casa.
In your sentence, gastar is the future subjunctive form.
Why does gastar look the same as the infinitive?
For many verbs, the future subjunctive looks identical to the personal infinitive or the plain infinitive in some forms.
With gastar:
- infinitive: gastar
- future subjunctive, eu form: gastar
So even though it looks like the infinitive, in Se eu gastar, it is functioning as the future subjunctive.
Some other forms make this easier to see:
- se nós gastarmos
- se eles gastarem
Those clearly are not just the plain infinitive.