Arabic Grammar Explanation: The Negative

	Positive	Negative
Past	I wrote	I did not write
ماضي	كَتَبْتُ	لم أكْتُبْ	فعل مضارع مجزوم       Imperfect Jussive
Present	I write	I do not write
مضارع	أَكْتُبُ	لا أَكْتُبُ	فعل مضارع مرفوع       Imperfect Indicative
Future	I will write	I will not write
مستقبل	سَأَكْتُبُ	لن أَكْتُبَ	فعل مضارع منصوب     Imperfect Subjunctive

*Note that لا has two functions.

1. It can be negative for the present tense (لا نفي) ‘I do not go’ and takes a dhammah on the verb.

2. It can be negative for a command لا نهي ‘Do not go!’ and takes a sukoon making the verb ‘majzoom’ jussive.

*Note that ما can also be used instead of لم to negate a negative verb. However the verb stays the same in the past:  كتبتُ/ ما كتبتُ I wrote/I did not write.
* ما can mean 'not' or it can mean 'what' depending on context. 'not' is negative but the 'what' makes the ما a relative pronoun.