Apologetics to the Glory of God

Not that again…?

Paul Manata wrote a post on whether or not TAG is a deductive argument here which Brian Knapp responded to here and then Paul wrote more here and here and here.

While I do not plan on jumping into the discussion, the readers may be benefitted by the somewhat lengthy discussion of this topic that I did engage in here and here and here and here and here and here.

My views now are not necessarily what they were then, but there are some points here that should be read in an effort to understand the texts from Van Til and Bahnsen on this issue.



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10 responses to “Not that again…?”

  1. Paul Avatar

    Was told that TAG had this form

    P presupposes CT

    P (or ~P)

    [C] CT

    And have been told you can affirm or negate P and still get CT.

    Can I get this printed out on a truth table? What is the logical symbol for ‘presuppose?’ Let’s call it +. So, I kow how –>, v, &, ~, , comes out on the truth table, how does + come out? Given what I’ve been told (i.e., the understanding of Bahnsen’s claim about “negating a premise,”), there is no truth table that can be given. Is this what those against TAG as deductive what to admit to?

  2. C.L. Bolt Avatar

    Well, I don’t, if that’s any help. 😀

    I don’t agree with Collett on this (anymore).

  3. Shotgun Avatar

    TAG: It’s not an argument, it’s an attitude.

    How can we put Christian theology into a truth-table?

  4. Peter Ochoa Avatar
    Peter Ochoa

    I am really mystified now. I have been following the discussion between Paul and CH but to me it seems somewhat unresolved. I go on IRC when I can to learn more but I can’t now so I was hoping for some clarification.

    I have commented on James Anderson blog at
    And one other post. James and Paul seem to be saying we don’t have certainty with a deductive arguement. Are we at an impass whether TAG is deductive? At this moment I see two brilliant groups coming to different conclusions. More information would be great.

  5. C.L. Bolt Avatar

    Bahnsen agreed with James and Paul that we don’t have certainty with a deductive argument. I would say the same thing. Bahnsen argues this point in his debate with R.C. Sproul. Of course, Bahnsen also claimed that TAG provides certainty, and so we have to conclude that Bahnsen, if consistent, did *not* believe that TAG was deductive. This is not to say that he was right. But then, Bahnsen also appeared to be speaking of *formally* deductive as opposed to merely deductive arguments.

    We run into a problem speaking about “TAG”. If Bahnsen presents TAG to us and Anderson presents TAG to us, and they are different from one another, which are we calling TAG?

  6. Paul Avatar

    “Of course, Bahnsen also claimed that TAG provides certainty, and so we have to conclude that Bahnsen, if consistent, did *not* believe that TAG was deductive.”

    That doesn’t follow, because the reason Bahnsen thought a deductive argument didn’t (necessarily) provide certainty was because of the knowledge of premises used in those argument, it wasn’t because of deductive *forms* of argument. Moreover, Bahnsen was more nuanced. He believed that some *Christians* might be able to have certainty from a deductive argument. For example, “all (mere) men are mortal, Socrates is a (mere) man, therefore, Socrates is mortal.” Bahnsen would argue that Christians have revelatory insight into the first premise. Also, with a deductive argument, *if* the premises are true and the form is valid, then the conclusion *must* be true. I can’t say Bahnsen would disagree with this, he’d just say, “Yeah, but how are we ever going to know whether the premises are true on the assumption that Christian theism is false.”

    Look, when we say TAG is deductive all that is meant is that it has the property of formal validity (i.e., that if the premises are true then the conclusion must be true), and can be written in a deductive form (i.e., premises that move from one to the other by rules of inference, each step justified by these rules). I claim that if this is denied then, as I tried to argue previously, you guys have a massive problem since no one has developed the “transcendental logic” by which we know whether any given transcendental argument is a good argument. We know nothing of the rules it uses to derive premises from other premises, whether the conclusion really follows from or is guaranteed by the premises. How would we know? Can you set two TAs next to each other and show rules that allow us to test and see where one went wrong and the other didn’t. Can there be bad transcendental arguments? Can they have a true conclusion but nevertheless reason poorly to that conclusion? How would we know?

    Anyway, the certainty denied is *epistemic* certainty, so it has nothing to do with form. Bahnsen would admit that if the premises of a deductive argument were true, then the conclusion would follow with certainty. He’s just going to deny that many (any?) of the premises can be known with certainty, and so the conclusion can’t be *known* with certainty. But from that it doesn’t follow that he denies that *if* the premises were true (or known with certainty to be true) that then the conclusion must be true (or known with certainty to be true).

  7. C.L. Bolt Avatar

    “the reason Bahnsen thought a deductive argument didn’t (necessarily) provide certainty was because of the knowledge of premises used in those argument”

    This is not *the* reason he thought it, but *a* reason.

    “it wasn’t because of deductive *forms* of argument.”

    At 37 minutes into the second file of the Sproul debate from http://www.cmfnow.com Bahnsen hits on just this point in response to Sproul’s comments about deductive or rational certainty. Bahnsen grants that the premises are true and still argues that certainty is not possible due to our inability to know for certain whether or not we have correctly applied (in this case) modus ponens and secondly due to our having to support our use of modus ponens in the first place through modus ponens.

    So I disagree with you on Bahnsen concerning this point, but I do believe there are inconsistencies in him as well. For example, only a few seconds later he says that even his apologetic arguments are not certain.

    In any event, I hope to study and write some on Bahnsen’s view of TAG as deductive or non-deductive or both in the journal we are trying to start. Hopefully I will have time then to track down some of the actual quotes, etc. from lectures and to read through your discussion with Brian as well (as I have not done so yet).

  8. Peter Ochoa Avatar
    Peter Ochoa


    What happens to the impossibility of the contrary in your view? Do you still agree that no other worldview is possible or other worldviews are possible and our view isn’t certain but more like the best?

  9. Paul Avatar

    Hi Chris,

    Been years since I listened to the Sproul debate. Anyway, I was made aware that you guys aren’t really doing “debates” in the comments section, so I won’t continue with the issue. I’ll just briefly say that your point one is still an epistemic matter and not an issue with the form. On the second, there are some people who take issue with material conditionals, and so he could be bringing up that discussion, but not necessarily thinking *all* deductive forms have said problem (in fact, they don’t), and so you’d need more than just that to get to the claim that Bahnsen thought *all* deductive argument did not guarantee certainty if the premises were true and the argument valid. Anyway, yes, if Bahnsen thought that *no* deductive arguments *guaranteed* the truth of their conclusions, but that TAG *did*, then that’d be good evidence that he didn’t think TAG was deductive. And that’d be even better evidence that he was wrong 🙂

  10. Paul Avatar

    Oh, let me add this: You don’t need modus ponens in a deductive system. All you need is ‘negation’ and ‘and.’ So I could grant his point ad arguendo, through out MP, and get all the same conclusions various repeated incidents of negation and conjunction, and the various rules applying to each. So i really struggle to see Bahnsen’s point.

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