his friend" is stative, while the past-tense verb in the sentence "Suddenly he understood what she said" is inchoative, because it means "He understood henceforth". On the other hand, the past-tense verb in "At one time, he understood her" is stative. The only way the difference between stative and inchoative can be expressed in English is through the use of modifiers, as in the above examples ("suddenly" and "at one time"). Likewise, in ancient Greek, a verb that expresses a state (e.g., ebasíleuon "I was king") may use the aorist to express entrance into the state (e.g., ebasíleusa "I became king"). But the aorist can also simply express the state as a whole, with no focus on the beginning of the state (eíkosi étē ebasíleusa "I ruled for twenty years"). Formal definitions In some theories of formal semantics, including David Dowty's, stative verbs have a logical form that is the lambda expression Apart from Dowty, Z. Vendler and C. S. Smith have also written influential work on aspectual classification of verbs. English Dowty's analysis Dowty gives several tests to decide whether an English verb is stative. They are as follows: Statives do not occur in the progressive: John is running. (non-stative) *John is knowing the answer. They cannot be complements of "force": I forced John to run. *I forced John to know the answer. They do not occur as imperatives, except when used in an inchoative manner. Run! *Know the answer! Know thyself! (inchoative, not stative; archaic) They cannot appear in the pseudo-cleft construction: What John did was run. *What John did was know the answer. Categories Stative verbs are often divided into sub-categories, based on their semantics or syntax. Semantic divisions mainly involve verbs that express someone's state of mind, or something's properties (of course, things can also be expressed via other language mechanisms as well, particularly adjectives). The precise categories vary by linguist. Huddleston and Pullum, for example, divide stative verbs into the following semantic categories: verbs of perception and sensation (see, hear), verbs of hurting (ache, itch), stance verbs (stand, sit), and verbs of cognition, emotion, and sensation (believe, regret). Novakov, meanwhile, uses the slightly different categories: verbs denoting sensations (feel, hear), verbs denoting reasoning and mental attitude (believe, understand), verbs denoting positions/stance (lie, surround), and verbs denoting relations (resemble, contain). Syntactic divisions involve the types of clause structures in which a verb may be used. In