An active or causal verb requires before it the instrumental instead of the nominative case, which goes only before a neuter or intransitive verb.
Thus intransitive bases seem to have begun only with soft consonants, and it is doubtful whether the parent tongue possessed hard consonants at all; while transitive bases were formed by hardening of the initial consonants and at the same time pronouncing the words in a higher tone, and these two latter changes are supposed to have been indicated by a prefix to the base-word.
In the sentence, The horse runs fast there is no object at all, so run is an intransitive verb.
Experiment 2 used potentially intransitive verbs in sentences like The boat floated down the river (and) sank.
And then 3 vi (verb intransitive) meaning verbs which do not take a direct object.
