What is the difference between an informal and formal command in spanish?

Question

I know this is informal 'Come tu Comida' but what would be formal?

What was edited? I removed the double quote marks around the phrase to make the question header more compatible with MS Explorer. - Moe, Nov 3, 2010

Answer 1

Come tu Comida as opposed to Coma su comida.

Using the Usted form, you change -er verbs to ending in -ar and vice-versa. And su is more polite than tu. So you could say, habla con tu tio (informal) or hable con su tio (formal). I do not, however, know if this rule works for everything and I don't know what to do with -ir verbs.

The imperative takes the same ending (is the same) as the present subjunctive (for usted) for all conjugations. - samdie, Nov 4, 2010

Answer 2

You didn't look at the answers to your previous question?

I believe that was third person and this is the difference between formal and informal. - Vince_Peña, Nov 3, 2010