Sunday, May 3, 2015

On Disagreement. Part 1

Suppose you’ve just completed an over 20-hour series of flights to an exotic location. You’re exhausted. When you get to your hotel, you close the curtains tight, curl up in a cool, crisply made bed, and finally fall into a delicious sleep. After what seems like an eternity, when you stir again, you crack open one eye and see that the bedside alarm clock reads 07:00 am. Refreshed and remembering that you have a busy day ahead, you pop out of bed, planning your day.

When you reach the bathroom to take a shower though, something strange catches your eye. The clock on the bathroom wall says 09:45 am.


Up until you walked into the bathroom, it was quite reasonable (ie. rational) for you to believe that it was 7 am. What’s it now rational for you to believe upon seeing the virtually simultaneous reading of 09:45 am on the second clock?

I don’t give a flying fruit what the actual time is, and I don’t mean for a second to suggest that if the scenario I just posed were to actually happen in real life, one ought to go back to bed and deliberate at length about the question I asked. There’s no doubt that you can just pick up the phone and ask the front desk what time it is, or check your smart phone that synchronizes automatically over WiFi. 


I care about what it’s rational to believe before sorting the problem out. Why? Because many disagreements that we regularly face are not so easily resolved and it is precisely those that are the most interesting and challenging disagreements to handle. For example:  “I thought we should pay down our mortgage, but my sister said it’s better to save for retirement.” “I really think I should marry him but my parents think otherwise.” “My cardiologist thinks I should put off having my valve replacement surgery, but the cardiac surgeon said that the operation is called for now.” I suggest that there might be something for us to learn from simple cases of disagreement that we might - no, we should - apply to the more complicated and important disagreements with which life is brimming.

So please stop and consider for a moment what impact the disagreement between the two clocks has on what one can rationally believe. Remember, you were rational to believe that it was 7 am right up until you saw the second clock. Should you (a) continue to believe that it’s 7 am, concluding that the second clock must be wrong? Should you (b) believe that it’s 9:45 and conclude that the first clock must be wrong? Should you (c) think that it’s probably half way between the two times (8:22:30)?  Should you (d) believe that you have no idea at all what time it is? Should you (e) believe that it’s probably morning?

You probably felt compelled to seek out further information as you contemplated the situation I posed, and that should be a good indication that (a) and (b) are not reasonable. After all, there’s no reason to think that one clock is more likely to be correct than the other. Perhaps it’s reasonable to believe that it’s morning, but notice that had the second clock read 7 pm, you’d be completely lost and you’d have to conclude with (d).

It seems obvious to me – a fact of rationality itself – that the awareness of the disagreement of the second clock must dramatically reduced the confidence that one rationally had in initially believing that it was 7 am. 

In Part 2, we’ll explore some more complicated disagreements, but this is an important time to chime in if you think that my conclusion is mistaken. I’ll repeat it one more time: the instant you become aware of the significant and mutually exclusive disagreement of the second clock, you have a very good reason to drop your belief that it’s 7 am. You suddenly have a very good reason to doubt that you can tell anything reasonable about the time, except that maybe, it’s morning, and that'll just have to do until you gather information that will settle the question. I think that if you agree with me here, you’ll have to admit that disagreement ought to have a much greater impact upon the confidence we have in our beliefs than it seems to have. Join me in the rest of this series on disagreement to see if I’m right, or if you disagree!


  1. An interesting question and in this case I agree with you. You have to be careful when the outcomes are not equally likely.

    If I may bring up Daniel Dennett and one of his 7 tools for critical thinking. (in this case #3)

    3. The “Surely” Klaxon

    A “Klaxon” is a loud, electric horn—such as a car horn—an urgent warning. In this point, Dennett asks us to treat the word “surely” as a rhetorical warning sign that an author of an argumentative essay has stated an “ill-examined ‘truism’” without offering sufficient reason or evidence, hoping the reader will quickly agree and move on. While this is not always the case, writes Dennett, such verbiage often signals a weak point in an argument, since these words would not be necessary if the author, and reader, really could be “sure.

    I am referring to your paragraph "It seems obvious to me". In this case I believe you to be ok, but it is a slippery slope from where you are on solid logical ground to the quicksand of logical fallacy.

    (the quote about Dennett is from here: )

    1. Thanks for your interest, Richard. My reply is in a separate comment below.

  2. Thanks for your interest, Richard. You hit the nail right on the head when you wrote: "You have to be careful when the outcomes are not equally likely." That is precisely the question that disagreement raises. Which opinion/idea/claim is more likely to be correct/true?

    The disagreeing clocks is a nice way to begin the discussion because it's hard to find good or strong reasons to think that one clock is more likely to be correct than the other. Without any such reason, the probability that either clock is correct cannot be better than 0.5 (after all, they both could be wrong). Further evidence or information is required to change that probability and permit assent to a rational belief about the time.

    I agree that my phrasing should make the “Surely” Klaxon go off. Thanks to your comment, I now realize that I could have added the following: “It’s not rational to hold both the belief that it’s 7 am and that it’s 9:45 at the same time, and since no good or strong reason exists for accepting the reading of one clock over the other, the awareness of the disagreement of the second clock must dramatically reduce the confidence that one rationally had in initially believing that it was 7 am.”

    The logic there is sound, and I’m sure (!) that it explains why we agree that I haven’t made a logical error.

    Thanks again, and I hope you’ll follow along as my consideration of disagreement gets more complex and interesting.