Information or resources on the correct use of "a"/prepositions with infinitive verbs

Question

When constructing sentences I am not certain whether or not to use "a" prior to an infinitive. Considering the infinitive itself means - to ____ :

To my understanding

"Voy a leer" - I go to read

"Quiero leer" - I want to read

"El sabe leer" - He knows how to read

Is every situation different? I am looking for an overall perspective on this issue/topic.

Thank you.

There is a similar post :

◾When to add prepositions before an infinitive verb (por/para/a/de)?

I am looking more specifically for how to know when or not to use "a" when in English one would say "to." Example -

"It is important to learn correctly".

how would that be translated - with or without "a" and, if time, why?

Might it be better to translate "Es importante que aprender correctamente" with que?

Otherwise, is it "Es importante aprender..." or "Es importante a aprender ..."

Each situation seems nuanced and maybe often requires other words such as "para", etc., or that often the English idea just needs to be restated/phrased in a "Spanish way."

Answer 1

Rule of thumb for learning any language with prepositions: learn the preposition along with the finite verb (the verb that conjugates: «voy a», «quiero», «sabe»): don't translate them.

Voy a leer. – I'm going to read. (compare: Voy a París. – I'm going to Paris.)
Quiero leer. – I want to read. (compare: Quiero agua. – I want water.)
Él sabe leer. – He knows how to read. (compare: Él sabe matemáticas. – He knows math.)

The same rule applies when the word or phrase preceding the preposition (or lack of) is not a verb.

Es importante aprender correctamente. – It is important to learn correctly.
(compare Es importante la buena presentación. – Good presentation is important.)

While in several sentences English and Spanish prepositions are directly translatable by their own, in many cases they are not. An the same is with Spanish and French, English and Italian, German and Swedish, etc.

For the use of English “to“ as either a preposition or an infinite marker, Gorpik already gave a good answer. Just a note in English:

• If you have a construction smth (with no preposition) plus verb, then verb uses the infinitive (the form with “to”):

  “I” + “to want” + “to drink” → “I want to drink.” – «Quiero tomar.»

• If you have a construction smth with preposition plus verb, then verb uses the gerund (the “-ing” form).

  “I” + “to live for” + “to party” → “I live for partying.” – «Vivo para rumbear.»

• Except if preposition is “to”, in which case the infinitive is used (the form with “to”) and the duplicated “to” is dropped.

  “I” + “to be going to” + “to read” → “I'm going to read” – «Voy a leer.»

Answer 2

First, the correct translation of Voy a leer would be I'm going to read.

Second, Es importante que aprender correctamente is incorrect; you don't use que in that situation. The correct sentence is just Es importante aprender correctamente or, better, Es importante aprender bien.

Now, to the main question. Movement verbs such as to go are usually followed by the preposition to and the place you are moving towards:

I'm going to London.

The kids went to school.

And the same happens in Spanish, but with the preposition a.

This is not so in non-movement verbs:

I want a new car.

I know the procedure.

The problem is that, in English, the infinitive is formed with to + verb. So you would sometimes need to use to twice; first the preposition, and then as part of the infinitive. In this case, the second to is omitted, so you may not notice that it is also used because of the movement verb, not just the infinitive. In Spanish this does not happen, so the preposition a remains even when used with an infinitive. With movement verbs:

Voy a Londres.

Los niños han ido a la escuela.

Voy a leer.

With non-movement verbs:

Quiero un coche nuevo.

Conozco el procedimiento.

Quiero leer.

Él sabe leer.