Differences between “aun”, “hasta”, and “incluso” to indicate extremes?

Question

When referring to an extreme example for comparison, English seems to have just one word, even:

Even an idiot could do it.

But Spanish seems to have three:

• aun
• hasta
• incluso

I had always used aun for this but then realized it wasn't the only possibility, such as in the old Shakira song, Octavo Día:

Hasta un ciego lo puede ver (Even a blind man could see it)

Does the choice of which to use depend on grammar or nuance, or is it purely up to the speaker's preference?

Answer 1

The three of them are correct as the RAE entry for incluso says:

incluso, sa.

(Del lat. inclūsus).

1. prep. Hasta, aun. Incluso a los enemigos amó. U. t. c. conj.

So they are synonyms. So you can say:

Hasta un idiota podría hacerlo

Incluso un idiota podría hacerlo

Aun un idiota podría hacerlo

No grammar rules apply, you can use any of them. All of them are used very often.

Answer 2

They are synonyms, however I'd say "hasta" is much more commonly used in hyperbole phrases. Thus:

• Even a blind person can see it. — Hasta un ciego puede verlo.
• Even your friend Johnny can see it. — Incluso tu amigo Juanito puede verlo.

Note, that you could switch them around and it would be still correct and understood. Only less commonly used.