How are the Arabic words katabtu and kutiba related?

In the Semitic languages, the Arabic words katabtu and kutiba are related through the root-pattern system, which is fundamental to Arabic morphology.12

Both words share the same consonantal root, √ktb, which conveys the general semantic notion of "writing". They are differentiated by their specific patterns—the arrangement of vowels and consonants—which assign distinct grammatical meanings to the root:12

• katabtu (katab-tu): This form utilizes the active past stem (katab-). The pattern indicates the active voice, and the suffix -tu functions as a subject marker meaning "I," resulting in the translation "I wrote".1
• kutiba (kutib-a): This form utilizes the passive past stem (kutib-). The specific vowel pattern (u-i) is used in Arabic to mark the passive voice, resulting in the translation "it was written".13

In this system, the root provides the lexical meaning, while the vocalic patterns and affixes determine the grammatical context, such as tense, voice, and person.12