Introduction

And this is eternal life, that they know you the only true God, and Jesus Christ whom you have sent.
(John 17:3)

I recently ran across an argument against the Jehovah’s Witness explanation of John 17:3, which is one of their primary proof texts used to attack the doctrine of the Trinity. Here the JW’s argue that since The Father is said by Jesus to be the only True God, then Jesus cannot also be the True God. The counter-argument is given as follows:

In fact, the entire argument that Jesus cannot be the true God based on John 17:3 is an example of a logical fallacy known as “denying the antecedent.”  To illustrate this point, let’s rephrase John 17:3b in the form of a logical proposition: “If one is the Father, one is the only true God.”

“If one is the Father” is the antecedent of the proposition.  “One is the only true God” is the consequent.  In the terms of formal logic, it is not logically valid to deny the antecedent, and conclude that the consequent is also denied. . . .

From the standpoint of pure logic, then, it is not valid to argue that because Jesus is not the Father (denying the antecedent in our paraphrased proposition) He cannot be the only true God.  Being the Father is sufficient cause for being the only true God; however, being the only true God is not a necessary cause for being the Father.

While I agree with the conclusion, there are a few problems here that could be exploited by one familiar with logic.

Problem 1: Stating The Argument

First, contrary to his stated intention, the above author is not translating the verse into logical language—rather, he is attempting to translate the Jehovah’s Witnesses’ argument concerning the verse. Now, the JW’s argument is basically that since The Father is the only True God, then Jesus (who is not The Father) is not the True God. The Watchtower puts it this way:

“Jesus prays to One whom he calls ‘the only true God.’ He points to God’s superior position when he continues: ‘So now you, Father, glorify me alongside yourself with the glory that I had alongside you before the world was.’ (John 17:5) Since Jesus prayed to God requesting to be alongside God, how could Jesus at the same time be ‘the only true God’?”

The argument, therefore, focuses on the fact that Jesus and The Father are distinct in some way – not necessary or sufficient conditions (note: not “causes”) for Godhood.

Problem 2: Proposition Translation

The second problem is that there is more than one way to logically translate this argument. For if there is only one God (which JW’s believe) and only one who is The Father (which JW’s believe), then being God and being The Father could be seen as necessary and sufficient conditions for one another. Since hypothetical propositions express the relationship between necessary and sufficient conditions, the phrase “If one is the Father, one is the only true God” works—but so would “If one is the only true God then one is the Father,” or even, “If and only if one is the only true God then one is the Father.” In either of these alternative cases the fallacy is avoided.

Problem 3: Argument Translation

The third issue concerns the fact that not only is there more than one way to logically translate this premise, there is more than one logic that can be used to translate it. When one is dealing with relations that obtain between propositions, then propositional logic (the kind employed by the above author) is appropriate. So, for example, the premise “If you clean your room then you can go to the party” expresses necessary and sufficient relations between the propositions “you clean your room” and “you go to the party.” So something like “If C then P” would be appropriate here.

However, arguments dealing with single terms in categorical relations to one another are best translated using categorical logic. Jehovah’s Witnesses do not seem to be claiming that being The Father is a necessary and sufficient condition for being the True God (in fact, I’d be surprised to ever hear a JW use such language!). Rather, they are simply saying that only The Father is in the category of the True God. Thus, something along the lines of “Since The Father is the only true God, and Jesus is not The Father, Jesus is not the true God” would be more appropriate. If nothing else, it is at least a possible interpretation—and when dealing with the arguments of others, the rule of charity says to choose the strongest possibility.

Now, in categorical logic the word “only” is a universal predicate indicator (e.g., the proposition “Only dogs make good pets” translates into “All good pets are dogs”). However, the phrase “the only” indicates a universal subject (e.g., the proposition “The only good pet is a dog” would also translate into “All good pets are dogs”).  Further, classes of one are considered to be universal singulars (e.g., “Doug Beaumont” would translate into “All things which are Doug Beaumont”). So, to get it into a form that can be more easily evaluated, we have the following:

1. All things which are the True God are things which are The Father.
2. No thing which is Jesus is The Father.
3. Therefore, no thing which is Jesus is the True God.

Evaluation of the Argument

Is this argument logically valid? Since it is a standard form three-term categorical syllogism, we need only ask three questions: (1) Do the number of negative propositions in the premises equal the number of those in the conclusion? Yes – there is one negative premise and the conclusion is negative. (2)  Is the middle term distributed? Yes – “The Father” is distributed in premise two. (3)  Are all distributed terms in the conclusion also distributed in the premises? Yes – “the True God” is distributed in premise one, and “Jesus” is distributed in premise two. For those who doubt my fantastic three-step categorical syllogism test, or who like pictures, here’s the Venn Diagram:

So, yes—the argument is formally valid.

Conclusion

Now, before anyone goes running to join the local Kingdom Hall, there are problems with the argument. Validity is only the first test for an argument’s worth. Soundness requires both that the argument be formally correct and that the premises be true. Here the argument fails in two ways.

First, the major premise begs the question. Whether or not more than one person can be the True God is the very issue at stake, so it cannot simply be sneaked into the premises as proof for the conclusion. While not a strictly logical fallacy, this informal fallacy destroys the entire worth of the argument (e.g., “Star Wars is the best movie ever because no movie is better” is a valid argument, but it clearly is not useful in a real debate for the conclusion simply restates the premise).

Second, the copula (“is”) introduces a philosophical problem: are we talking about the person or the essence of The Father / True God when we say what Jesus “is”? Jesus not being the same person as the Father does not exclude him being the same essence as The Father–namely, that of the True God. This, of course, is precisely what orthodox Christianity asserts. JW’s seize on their own misunderstanding of the person / essence distinction to make their argument appear sound, when in fact their argument relies on the very confusion declared heretical by orthodox Christianity (cf. The Definition of Chalcedon below).

We, then, following the holy Fathers, all with one consent, teach men to confess one and the same Son, our Lord Jesus Christ, the same perfect in Godhead and also perfect in manhood; truly God and truly man, . . . consubstantial with the Father according to the Godhead, and consubstantial with us according to the Manhood; . . . to be acknowledged in two natures, inconfusedly, unchangeably, indivisibly, inseparably; the distinction of natures being by no means taken away by the union,