As a general rule the vast majority of Tibetan verbs reside within two categories, those which express implicitly or explicitly the involvement of an agent, marked in a sentence by the instrumental particle ( (kyis), etc.) and those expressing an action which does not involve an agent. Tibetan grammarians refer to these categories as (tha-dad-pa) and (tha-mi-dad-pa) respectively. Although these two categories often seem to overlap with the English grammatical concepts of transitive and intransitive, most modern writers on Tibetan grammar have adopted the terms "voluntary" and "involuntary", based on native Tibetan descriptions. Most involuntary verbs lack an imperative stem. Refer w:Classical_Tibetan#Verbs