The converb -las in Old Tibetan

In contrast to its description in available grammars and manuals, the converb -las in Old Tibetan is used primarily to mark off the following clause as surprising given the background of the preceding clause. The converb -las enters into two distinct syntactic constructions: after a reduplicated verb it indicates the interruption of a continuous event; and in a three-clause pattern with the converb -kyis, -las introduces a surprise or contrast in the second clause, but -kyis in the third clause returns the sentiment to that of the first clause. Although the examples which demonstrate the use of -las are drawn from Old Tibetan texts, this use continues in later texts.