The past tense
Arabic · Key Stage 2 · The School
The dictionary form is a past-tense verb
Arabic verbs are listed in dictionaries in their simplest past-tense form: he did. Kataba means he wrote, three root letters with short vowels between them. That form is the starting point for everything else, which is why looking a verb up gives you a whole word rather than an infinitive as in English.
The ending names the doer
Arabic does not need a separate pronoun, because the ending carries it. Kataba is he wrote; katabat is she wrote; katabtu is I wrote; katabna is we wrote. The root stays visible throughout and only the ending moves. This is why an Arabic sentence can be a single word and still be complete.
Past and present are built differently
The past tense marks the doer with an ENDING. The present tense marks it with a PREFIX at the front, which you have already met — yaktubu, he writes. So the two tenses are told apart by where the information sits: look at the front for the present, and at the back for the past. Once you see that, most verbs become readable.
كَتَبَ he wrote. كَتَبَتْ she wrote. كَتَبْتُ I wrote. كَتَبْتَ you wrote (to a man). كَتَبْتِ you wrote (to a woman). كَتَبْنا we wrote. The stem كَتَب never changes; everything is in the ending. Compare with the present, where the information sits in a PREFIX instead — past adds at the end, present adds at the front.