Still working with examples of "a" before a noun/D.O.?
Context: In my Spanish 101 class workbook the sentence is:
Mi hermanita aprende a bailar.
Question:
In this instance I understand in Spanish "bailar" is a verb, not a noun. So why is the "a" used before "bailar"? Has it got something do with "bailar" being a direct object of the main verb "aprende"?
8 Answers
The "a" is needed because of aprender.
From Spanish for Dummies:
When a Spanish sentence combines a conjugated verb with an infinitive, there are certain verbs that require the preposition a, de, en, or con before the infinitive verb form. Other Spanish verbs are followed immediately by the infinitive and don't require a preposition.
The list of verbs requiring a "a" includes:
aprender
ayudar
correr
ir
salir
venir
The book lists about 25 of these common verbs. I listed only a few, for illustration.
The words requiring "a" before a following infinitive are generally those that express beginning, motion, teaching, or learning.
Example:
No empieza a llorar (Don't start to cry)
This is a very revealing discussion. Thanks guys.
Pesta. This is another example of the mystery I'm wanting to solve. Do the words in your list of verbs that do require a preposition between them and a following infinitive follow a grammatical "rule" which applies to all of them. If so, I would like to find it. Otherwise, it seems arbitrary and apparently they (words of one type or the other) can only be learned by trial and error and memorization of the specific word(s) which are "given" in some printed sources which present lists of at least some of them. When I see a list of them, similar to what you apparently have, I've not seen any statement or assurance as to whether it is substantially complete, partially complete, or only a sample of some commonly used. As a result I have to look carefully at each new verb - and again at those I don't remember - when I use them to try to determine if they should or should not carry the appropriate preposition. I did see you said those that do are usually indicating motion, beginning, teaching or learning. Did you just notice that fact, or was there some discussion of it in your book?
Otravez: I hope you don't mind my two cents worth. As you can tell by my questions many new learners are having difficulty with the "a". When to use it or not to use it alI. With what Pesta is sharing this list is arbitary as far as I can tell. Some books, texts, professors will let a student in on a few at a time. So one forum member suggested any time a new verb and how to use that verb is introduced they update either a flashcard or an excel spreadsheet or whatever works to keep the darn verbs straight. Hope this helps some!
I found this rather complete page of information:
The rules they summarize are:
Verbs meaning “to begin” and verbs of movement towards someplace or goal are normally followed by a plus an infinitive.
Verbs meaning “to stop” or “to finish” are normally followed by de plus an infinitive.
Modals (e.g., “should”, “can”, “may”) are normally followed by an infinitive with no intervening preposition.
Verbs meaning “to continue” are normally followed by the -ndo form, with no preposition.
You can simply memorize these. There are only a few hundred. 
Not sure this is any help but.........
Some English verbs have to be followed by an infinitive - some don't and some can be followed by either the infintive or the gerund.
Examples
Listen to me - but not - Hear to me
I want to eat pizza
I like to eat pizza OR I like eating pizza
I enjoy eating pizza - normally not - I enjoy to eat pizza.
I know of no list that provides such verb explanations.
As I copied from the Dummies book,
The words requiring "a" before a following infinitive are generally those that express beginning, motion, teaching, or learning.
The other categories (de, en, or con) were not described by a pattern to indicate their use. Of the common verbs taught in this book, the list requiring "a" was the largest (about 25 verbs), and de's list was smaller, en's list even smaller, and con's list was the shortest. They wrote that you have to memorize these, as there was no rule for them.
They also included a list of verbs that are followed by infinitives without a preposition (for example, querer, ir, etc.).
I don't have the book handy right now, and I don't have handy web links. But I can confirm the bad news: There isn't any better rule than you see here. Sorry :(
I have found from the library Barron's Spanish Pronouns & Prepositions by Frank Nuessel, Ph. D. In his discussion about the preposition "a" he talks about the "a" being needed to indicate movement or direction after certain verbs. I think Pesta is saying beginning, teaching, learning can also be an indicator as to when the verb needs the "a".
Corrections to my reasoning is always appreciated.
