中文摘要：

中古藏语具有yin、lags和red三个系动词，同时它们还兼做助动词。red至迟不晚于14世纪语法化为系动词，它打破了古藏语yin和lags表“统称～敬称”的平衡，而使藏语逐步过渡到yin和red表“向自我～向他者”示证范畴的对立。

英文摘要：

In Middle Tibetan, there are three copular verbs yin, lags and red, which can also act as auxiliary verbs. No late than the 14th century the content verb red has grammaticalized into a copular verb, and this grammatical change imparts unstability to the semantic system of generic versus honorific conveyed by the copulars yin and lags in Old Tibetan. Thus, in Modem Tibetan copular verbs yin and red come to mark the evidential distinction of egophoric versus heterophoric.