 The serial construction also serves as the structure for a number of compound expressions of tense, aspect and modality, e.g.But there are also constructions, or variant expressions, that depart from this pattern somewhat.The invariable word "katka", which means 'was' or 'before, in the past', may occur following a verb form to establish past or habitual reference, e.g., "inte kimati katka" 'he didn't know'.