Future tense verb vs Ir + a + infinitive

[luis magistrado]

Is there a rule on how to chose the more appropriate form of the future tense between the conjugated IR + infinitive and verb conjugated in future tense? For example, if i have to choose between "Voy a viajar" and Yo viajaré , are the two ways of expressing the future interchangeable in all context?

Thank you in advance.

[Rusty]

The difference is the same as in the English "I'm going to travel" and "I'll travel."

In other words, when you would use "I'm going to do something" in English, use it in Spanish. Likewise, if "I'll do something" is what you would say in English, say it the same way in Spanish.

[wrholt]

The synthetic future (viajaré, etc) and the periphrastic future (voy a viajar, etc) are mostly interchangeable, but there are contexts where they are not interchangeable.

The most common context where only one of these forms is permitted is sometimes called 'future of probability': the use of the synthetic future to state what the speaker believes to be the most likely current event or state.

For example, suppose your friend María says: "¿Qué sabes de José? Suele ir a trabajar en el mismo autobús que yo, pero no lo he visto desde el viernes pasado."

If you talked with José last week and he told you that he was going to go on a business trip this week, you could say: "Está en un viaje de negocios." The simple present indicative implies that you are stating something you know to be true.

However, if José never mentioned anything to you, but you know that he travels for business several times a year, you might say: "Estará en un viaje de negocios." = "He must be on a business trip", "He probably is on a business trip". In this case using the synthetic future indicates that you do not know as a certainty, but you have reason to believe what is likely to be the current state. There are other ways to express the same idea without using the 'future of probability', of course, but this usage is relatively common.

[chileno]

Ir a inf = inf

Qué te gustaría hacer?

Ir a viajar por el mundo = viajar por el mundo

[cesar ortiz]

Como probablemente se habrán dado cuenta por mis comentarios, vivo en Argentina, así que normalmente utilizo el español rioplatense, que tiene sus particularidades. Aunque en este caso estamos alineados con el resto de los hispanohablantes. Aquí casi siempre usamos "ir" + a + infitivo, el Futuro Simple es demasiado formal y no expresa la intención. "Con la expresión "ir" + a + infinitivo expresamos una acción futura ya planificada frente al Futuro Simple, con el que expresamos un anuncio de una acción futura no planificada". Ej:" Vamos a ir a la discoteca" (planificada) e "iremos a la discoteca", (no planificada).

[luis magistrado]

Thank you.

Your responses are very enlightening.