Modalism has evolved into something more difficult to fight against. Initially it made a simple claim that the one God simply manifests his person differently at different times; sometimes as Father, other times as Son, other times as Spirit. “Father”, “Son”, and “Spirit” were all held to ultimately be different names for the same person.
This is a fairly obviously false doctrine and its not a heresy that’s hard to disprove. The scriptures clearly speak of the persons of the Trinity (the Father, the Son, and the Spirit) as three distinct persons. There is such an abundance of these instances that I think it is not even necessary to cite any here. A cursory reading of the Bible makes it perfectly clear that the Father is not the Son, and the Son is not the Father, nor are they the Spirit nor is the Spirit them. They are three truly distinct persons, united in will and action, and eternally inseparable from one another; but truly distinct nonetheless.
Semi-modalism is the next variation of modalism to sweep the church and it is significantly more crafty and dangerous. It hides behind orthodox language to sound as close to orthodoxy as it possibly can. It keeps the fundamental tenet of modalism unchanged- that the one God is one person, who somehow turns out to be Father, Son, and Spirit. But instead of saying they are just modes or roles he takes at different times according to his will, they say that he permanently, or even by nature, exists as all three at the same time. This one person manages to eternally exist as three persons, according to the thinking of the semi-modalists. The next trick they pull: deny that the one person is a person.
In doing this, they sound totally orthodox. They can say that they really believe in nearly everything an orthodox trinitarian does. Do they believe in three distinct persons? Absolutely, they say. Do they hold them all to be co-essential, that is, of the same divine nature? Yes. Do they hold that all three are co-eternal and inseparable from one another? Yep. They sound nearly perfectly orthodox.
But their blasphemous error can be revealed not simply by asking what part of the truth they don’t believe, but what they add to it. They believe in three distinct persons, Father, Son, and Spirit. They say they believe in the Trinity. But they also believe that the Father, Son, and Spirit are all one person. They usually don’t use that language, because they know it sounds heretical and insane to say that the one God is one person who is three persons. But they do in truth believe that, and think of God that way.
What evidence can be seen to give this away? One of the greatest things that shows this is their persistent use of singular personal pronouns for all three persons of the Trinity as a group. If the Father, Son, and Spirit are three persons, then they are referred to, according to the rules of grammar, by the term “they”: a plural personal pronoun. This is consistent with the fact that there is a plural number of persons- namely three. But when the semi-modalist refers to the three persons together they are referred to as “he”. “He is Father, Son, and Spirit” they will say of the one God.
They will call this person by certain names. Some of old called him “God the Trinity”- clearly marking their belief that the Trinity, that group of three divine persons, is itself a single person. Today the name “triune God” is in vogue. They will speak of this “triune God” always as a person, but nearly never openly admitting that he is such. Most will openly deny it if they are questioned. But they always call this “triune God” “he” and “him”: always singular personal pronouns are used. This betrays their true belief.
A few of these heretics have been so brave to come out and openly say that they believe the Trinity is a person. Cornelius Van Til did. He was rightly criticized as being a heretic; yet many of those criticizing him have nothing to boast in as being any better than him except that they do not come out and openly say what they think, but are determined to mask their belief behind orthodox language. Their denials betray the fact that their belief is shameful. Their inconsistency is obvious. They call him a heretic for saying openly that the Trinity is a person while they themselves constantly refer to the Trinity as a person by referring to it with singular personal pronouns.
What must be looked at here is not merely verbage, although the words used certainly matter a great deal, and must be contended for. But what is actually believed must be examined. These false teachers are experts in twisting words to serve them and sounding like they are orthodox. But the substance of their belief, when you get down to it, is that the one God is a single person they can interact with, worship, glorify, and pray to, who is himself both the Father, the Son, and the Holy Spirit. The heart of their belief is not different than that of classical modalism. It has simply evolved, and its fooled so many. Don’t be one of them.
The Bible is really quite clear concerning who the one God is, and its really among the most basic doctrines of Christianity. Yet it seems that in some circles a knowledge of it is nearly lost. The one God is the Father (1 Cor 8:6, Eph 4:6). The one God is a person: He is a “He”. The error does not lie in thinking of Him and interacting with Him as a person; the problem lies in failing to recognise that person as the Father. He is the one who is the eternal Father of the Son, and the adoptive Father of all the saints. That is Who the one God is. That’s what’s missing from most people’s’ formulation of trinitarian doctrine. That’s what the semi-modalists lack that they require.
Want proof the one God is the Father, from scripture? Check out my post on that topic for explicit proof from scripture and historic testimony from the ancient Christian church. This doctrine is biblical, and was taught by the early church; see for yourself at: https://nicenefaith.wordpress.com/2017/03/08/i-believe-in-one-god-the-father-almighty/