Semi-modalism is the false doctrine that teaches that the three real persons of the Trinity are together a single person. Most semi-modalists, however, refuse to use the term “person” for the Trinity, although conceptually they treat the Trinity as a whole as a person in every way except using that term for it.
Twentieth century theologian Cornelius Van Til is a noteworthy figure in the history of theology. Many of his ideas were and continue to be highly controversial, especially in the area of apologetics.
But Cornelius Van Til is lesser known for something perhaps even more remarkable than his apologetic methodology- his views regarding the Trinity. They have, to be sure, garnered some attention- but probably not the amount they deserve. This is because Cornelius Van Til boldly went where other theologians who he is essentially in agreement with never went before- he came out and called the Trinity a “person”.
If you ask anyone how many persons there are in the Trinity, they will likely tell you there are three. This is obvious- the very word “Trinity” comes from ‘Tri’=three, combined with ‘unity’, meaning three in unity. Three persons, of one essence, as the classical formulation goes.
Sadly though, if we actually take the time to examine how many persons many so-called trinitarians believe in, we will quickly see that there is an extra person afoot. This is because many theologians who have succumbed to the lies of semi-modalism have accepted the Trinity itself as a fourth person. These people take the one essence, or divine nature that is supposed to be shared by the three real persons of the Trinity and imagine it to be a person itself. Another variation of this is to simply imagine that the group of three persons is a single person. By personifying either the group of persons or the divine nature, these false teachers have craftily introduced a fourth person into the Trinity.