A controversy prevails in the study of Semitic languages, both ancient and modern, namely whether their verbal morphologies mark tense (e.g. past vs. non-past), or aspect (perfective vs. imperfective), or some combination of both. Also something of an issue are and modality, but they are not usually as problematic (or they are problematic in different ways) as tense and aspect.

Arabic is consistent with other Semitic languages in its nonconcatenative morphology. Verbal and nominal forms alike are typically formed by interdigitation of consonantal roots (ideally c…