First post. I just have a question about identifying a fallacy.

Let's say you are talking to someone who believes the earth is 6,000 years old. You begin to present evidence that suggests the earth could not be 6,000 years old and the person responds that 'we just have different presuppositions' and further explains that you are listening to some experts while they are listening to others. They say you are just as biased about your beliefs as they are (Tu Quoque fallacy) and that it all depends on your 'worldview'.

So obviously we have a Tu Quoque in there but I'm not sure about this idea that everyone just has a 'starting point' and that affects everything. It seems to completely ignore the scientific method and treats evidence as if it's equivalent to bias. I'm thinking a Subjectivism Fallacy? Any thoughts?


  • 2
    I usually skip the fallacies. I find all they do is make us feel smart, but they're not that good at winning arguments. I'd recognize that you can't force someone to change their opinion. Instead, I'd skip up to the meta discussion of how we interact with others. You have to explore how we interact with others when we come from the position of vast consensus, while your fellow debater needs to explore how to interact when you come from the underdog position. How do we find common ground while trying to accomplish these two goals?
    – Cort Ammon
    Commented Jun 22, 2017 at 20:08
  • Thanks Cort Ammon. That's a very good point. I should reveal that I used to be a young-earth creationist not so long ago and I'm kind of asking this questions in an effort to improve my 'mental algorithms'. I'm just exploring what is the best/logical way to think. That being said, I like your points about finding common ground.
    – hobeau
    Commented Jun 22, 2017 at 20:22
  • i'd suggest instructing them they're not involved in a mere performative contradiction (i think?) but are being incoherent. then deny the tu quoque. though obviously you lose @CortAmmon's "common ground", which may be a problem
    – user25714
    Commented Jun 22, 2017 at 21:19
  • "Everyone is biased" is NOT a fallacy, it is a true statement. The difference comes from the type and degree of bias each one of us has. The misuse of this "truth" to justify a person's point of view or position, is the fallacy.
    – Guill
    Commented Jun 27, 2017 at 18:41

3 Answers 3


This kind of approach would declare the whole of Scholastic philosophy one big fallacy. And it would be unfair to go that far. Rejecting your sources of authority, and adopting their own is not a fallacy.

But it does excluded them from the cultural mainstream in a way that is ultimately not maintainable. For instance, 'Biblical archaeologists' happily use carbon dating, which they cannot consider valid evidence if they reject other deductions from carbon dating...

You end up back at the point where light was not refrangible by water before The Flood, because rainbows came into existence at a recorded point in Biblical history. So God just changed physics, at least twice. And that means nobody has any evidence. Who can argue?

  • Hi Jobermark, thanks for the response. Let me ask the question in a different way. At some point the Ptolomaic model of the Cosmos was observably wrong and the Copernican system had sufficient evidence to demonstrate it was a superior theory. Wouldn't it be fair to say at some point it is no longer true to say that both models are a matter of perspective and to say so would be a false equivalence? Or am I confusing that with Warrant? Thanks again.
    – hobeau
    Commented Jun 22, 2017 at 20:07
  • Based on basic principles of science, yes. But one is not somehow formally obligated to accept basic principles of science. Using them sometimes and contradicting them other times is intellectually dishonest. But doing without them altogether is not a fallacy of any sort.
    – user9166
    Commented Jun 22, 2017 at 21:34
  • Our legal system has a principle that eye-witness testimony and repeatable memory are the most reliable sources of information. Science disagrees, entirely. Yet no one insists that this means people convicted under the current rules of evidence are wrongly imprisoned. We simply choose to ignore the science because we have a couple centuries of precedent, and precedent is the most basic way to make legal decisions in our system. This is bizarre, but it is not a logical fallacy.
    – user9166
    Commented Jun 22, 2017 at 21:40

I imagine that from his perspective, and I'm not agreeing with this, your bias is your presupposed (assumed without proving) beliefs about truth, namely that the only way to prove the truth of something is through scientific principles and that any other type of proof is invalid. So you'd have to somehow explain why your system of truth through science is better than his system of truth through whatever.


If everyone is biased, then this includes not only you but the person who makes the claim that everyone is biased.

In any case 'we just have different presuppositions' does not entail that we cannot check our and others' presuppositions for consistency, clarity, economy, and evidential-fit unless (what does not at all follow) our different presuppositions specifically involve different ideas about the criteria for consistency, clarity, economy, and evidential-fit. We can disagree about the age of the earth without disagreement about these criteria.

Also, bias is not determined by 'different presuppositions'. We can share the same presuppositions but I can argue in a biased way without your doing so.

Bias is connected with truth, or accuracy, or correctness, or adequacy: to the extent that something, or someone, is biased, it or he or she is unlikely to be right, or accurate, or correct, or adequate. Bias prevents or inhibits one in the quest to attain truth. (This explains at least one reason that bias is undesirable, and that we ought to avoid, or minimise, bias if we can. (Jim Mackenzie, 'Two Images of Bias', Oxford Review of Education, Vol. 23, No. 4 (Dec., 1997), pp. 487-502 : 490.)

Seen in this way, not only can we share the same presuppositions but one of us argue biasedly and the other not, we can have different presuppositions and both argue in an unbiased way, genuinely seeking truth, or accuracy, or correctness, or adequacy within the frameworks of our different presuppositions.

In a word, different presuppositions are neither necessary nor sufficient for bias.

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