when to use the future tense and not the subjunctive

Question

For a piece of homework I had to write a short essay.

I wrote the line below and when I was going through it with my teacher I thought she would say it was incorrect. The reason I thought it was incorrect was because I was talking about my opinion so thought I should have used the subjunctive.

Creo que acelerará el uso de más tecnología remota

My teacher did explain why it was correct to use the future tense in this case however being old I have forgotten the reason which is rather annoying.

Why is the subjunctive not used here?

Answer 1

We use the indicative to express opinions, as long as the opinion verb is in positive form:

Creo que acelerará.

Creo que viene.

Creo que va a venir.

Or even (as the opinion verb is still in positive form):

Creo que no acelerará.

Creo que no viene.

Creo que no va a venir.

We use the subjunctive to express opinions in negative form:

No creo que acelere. / No creo que vaya a acelerar.

No creo que venga.

No creo que vaya a venir.