"Escribe tu nombre."
Translation:Write your name.
That's a good question. "Escribe" is the imperative form of "escribir", but it is also the Usted/El/Ella form.
You can rule out Usted as an option, because you don't use Usted and Tu forms in the same sentence, so "You write your name" is not a valid translation.
However "He/she writes your name" are valid translations (but I don't know whether DuoLingo recognises them).
"For most verbs (regular and irregular) the affirmative form of the familiar tú command is the same as the él form of the present tense. Familiar command endings are: -a for -ar berbs; -e for -er and -ir verbs." Por ejemplo ¡Saca una foto del museo¡ ¡Lee el libro de español! ¡Pide una CocaCola par mí también!
En la 4ª advertencia a los "Modelos de conjugación verbal" la RAE indica en el Panhispánico:
"En el imperativo, solo se registran las formas propias, esto es, las correspondientes a la segunda persona del singular y del plural."
Por otro lado, se puede leer en el apartado 42.2.1 "El imperativo. Sus propiedades formales" de la Nueva gramática de la lengua española. Manual:
"... Desde el punto de vista morfológico, este se caracteriza por presentar un paradigma defectivo constituido fundadamente por formas de segunda persona. Así, por ejemplo, el imperativo del verbo venir consta de las siguientes formas:
SINGULAR: ven ~ vení (en las zonas voseantes), venga (usted). PLURAL: venid (usada en parte de España, vengan (ustedes), vengamos"
En las tablas en 4.9 de la misma obra, sólo aparecen dos formas para el imperativo. Etc, etc.
Como todo en una lengua es algo más complicado que uno y uno son dos, pero las formas exclusivas del modo imperativo son las de segunda persona.
¡Tiene razón¡, Highways. The various forms of "you" (tú, Ud., vosotros/as, Uds.) are the most common forms of the imperative. When I first learned this tense, I was surprised to learn that there is also a "nosotros" form. It is a command to a group of which "you" are a member, it uses the 1st person plural subjunctive form, and it is translated as "Let's." Although it is probably more common (and easier) to use "Vamos a" + infinitive to express this, the nosotros imperative form does exist and is listed in all conjugation books and sites. However, "¡Vámonos!" is the only word in this tense that I can recall ever having heard in speech.
http://www.123teachme.com/spanish_verb_conjugation/escribir http://www.spanishdict.com/topics/show/91 http://www.cliffsnotes.com/foreign-languages/spanish/spanish-ii/the-imperative/nosotros-lets-commands
This link is helpful but this seems so complicated! So an imperative means a command? And you don't use the "normal" verb rules? I, too, would have used "escribas" but what I get from this is that in a command you use the he/she form when you are saying a command to someone?
Yes, imperatives are commands. And yes, Spanish conjugation is definitely more complicated than English, but at the same time English conjugation is a lot more complicated than we realize because it comes naturally to us now.
Think of all of these: write your name; you write your name; you wrote your name; you would have written your name; you had written your name; you will have written your name; etc. We use the verb a little differently in each of these cases, and so does Spanish: http://www.spanishdict.com/conjugate/escribir
Like you, I also tend to think of the second person singular imperative being the same as the third person singular present indicative (present indicative is the "normal" conjugation we learn first in Spanish), but that's not always the case since some verbs are irregular. For example "you say your name" is "dices tu nombre", but "say your name" is "di tu nombre". http://www.studyspanish.com/lessons/irregtucomm.htm
To complicate all of this further is the fact that negative commands are also different, though spanishdict doesn't seem to list them in conjugations for some reason. For example "don't say your name" would not be "no di tu nombre", but rather "no digas tu nombre". http://spanish.about.com/od/verbmoods/a/negative_commands.htm