Think about it this way: In English, the Future Phrasal for "What are we going to eat?", has the infinitive, "to eat" with the "going", as in "going to eat". So perhaps it is not too surprising when you think about it, that in the Spanish Future Phrasal, we have vamos (going) + the Spanish infinitive "a comer". So, we have "vamos a comer", just like we have in English, "going to eat". :-) So the Future Phrasal, both in English and in Spanish, follow the same formula: "Going + infinitive of the verb" to mean "Going to do something in the future". That is why they call it a Phrase, because it needs "going" plus the infinitive to make a Phrase taking about the future. There is still the Future conjugation. But, I think using "going + a verb infinitive" is easier to learn.
An introductory textbook to the jurisprudence course at one of the Oxford University colleges had a more nuanced view of this. I/We shall and others will is supposedly correct as you say, but this is reversed when there is an implicit command or an expression of determination, e.g. "We will remember them" (the War dead) or "you shall do your homework, or I will beat you". The claim was also made that the position is reversed in Scottish English.
This was in "Learning the law" by Glanville Williams, now in its fourteenth edition I see, but not when I read it!
Point me to the page where Duolingo explains that. If it's not included it should be. It's a free program and that's great. But it seems a student has to consult the discussion pages for a lot of additional info. It still doesn't seem right. "a" is to and 'comer' is to eat. I am going to TO eat???
You have to remember that duolingo teaches by having you work through the examples rather than by explaining the lessons . And as far as adding the "a" as well as "comer" is just one of those things that you have to learn. you can't always translate word for word for word.
Gael, like Ruth said, DL works via examples. There are tons of other resources online to learn grammar + rules.
I want to add that in this sentence the "comer" doesn't stand for "to eat" specifically. It's more like "eating" or the act of eating. So the "a" = to (or for) the action. Vas a entender, ¿sí?
Perhaps 3 years ago, DL Spanish did not have "IR Future" Notes and Tips. But, just for the record, you can find an explanation about Phrasal Future in the "branch" of the Spanish Language tree, called "IR Future", and if you click on the light bulb icon, it brings up: " Verbs: Phrasal Future Tense Tips and notes Phrasal Future There are two future tenses in Spanish. The easier one to learn is the so called "phrasal future," in which the verb "ir" (to go) is used an auxiliary. Much like in English, where you can express future by saying "I am going to run tomorrow," in Spanish you can say "Voy a correr mañana." Thus, the future is formed by conjugating the irregular verb "ir" to the appropriate person, then adding the word "a," and then the infinitive of the main verb. Below are the conjugations of the verb "ir," followed by examples of phrasal future...." Note, many of the "branches" of the language trees have Notes and Tips available through clicking the "Light Bulb" icon when you are working on a "Level", I hope this helps future students.
"which are we going to eat" should be accepted as in pointing to two different cupcakes and asking which are we going to eat. Qué can be which as well as what. Descubrir qué instituciones son adecuadas para las condiciones locales requiere de experimentación. Discovering which institutions are suitable to local conditions requires experimentation.