what is the difference between the negative tú command and the affirmative tú command?

Firstly, the most obvious difference is that negative tú commands are preceded by a negative word such as 'no' or 'nunca'. These two types of tú command also differ in the way that they are formed grammatically. With affirmative tú commands, the third-person singular form of the present indicative tense is used. With verbs ending in -ar, the infinitive ending is removed and the third-person singular '-a' ending is added to the stem. For example, if we take the verb 'comprar', the affirmative tú command of this verb is 'compra'. With verbs ending in -ir or -er, once again the infinitive ending is removed and the third-person singular '-e' ending is added to the stem. For example, the verb 'escribir' becomes 'escribe' when the affirmative tú command is formed and for the verb 'aprender', the affirmative tú command form is 'aprende'. In order to form negative tú commands, the present subjunctive tú form is used which therefore involves a change in the conjugation vowel. For example, with regard to verbs ending in -ar, the infinitive ending is removed and the second-person present subjunctive '-es' ending is added to the stem. For example, the verb 'comprar', becomes 'no compres' in the negative tú command form. With verbs ending in -ir or -er, again the infinitive ending is removed and the second-person present subjunctive '-as' ending is added. This means that the verb 'escribir' in the negative tú command form becomes 'no escribas' and the verb 'aprender' becomes 'no aprendas'