The above examples of verbs illustrate two other kinds of verb: ergative and normal verbs. Unlike in the discussion of noun cases, ergative verbs refer to events that take place within or are directed towards the verb's subject - that is, the instrument of the verb is the subject. The verb "sees" in the second example is one such verb, as are "to think" and "to believe". They often take complementizers. The normal type of verb indicates that an action is exercised against the verb's subject; these verbs often require an object in order to be grammatical. "Lifted" above is one example of such a verb; an English speaker would be put off by an adult saying *"I lifted" - the instinctive reaction is "You lifted what?".
Some verbs, like "eat" can be used either way. It is perfectly legitimate to say "I ate.", in which case it is ergative - because the action affects only the subject of the verb, whereas "I ate a salad" describes what has been eaten.
There are languages which distinguish verbs based on their ergativity and/or their transitivity, which suggests that these are salient linguistic features.