a bit more about that Descartes stuff

so the other day I talked about Descartes and the idea that we can’t really know with 100% certainty that what our senses tell us is true.

One of the commenters on my post on g+ responded:

Testable. Observable. Repeatable. Independently verifiable.

I toss a rock into the air, it falls. You toss a rock into the air, it falls. The rock falls whether I am looking or not. Your rock falls whether I am present or not. These observations can be recorded, exchanged, and define a shared reality.

which sounds great – we’re so used to regarding this as the way to verify objective truth that we don’t see the limitations of this method. My senses tell me that the rock falls. My senses tell me what the records of observations are saying. My senses tell me that I’m looking at a piece of paper on which someone else has written a record of their own observation. My senses tell me that another human being is standing in front of me and speaking, telling me their own observations of a rock falling. All these corroborations – they could all be part of my hallucination. So how can I really know for sure?

The answer is we can’t. There’s no way of evaluating our sensory perception without using our sensory perception, and we know that our senses can (and sometimes do) mislead us.

And yet, I do rely on my sensory perception in day to day life – we all do, because we need some kind of working assumption. We can’t go around with a constant awareness of this uncertainty. We regard it as reasonable to rely on our sensory perception, and I’d like to make it very clear that I’m not for one minute suggesting it isn’t reasonable. When I look out the window and see sunshine I don’t say “I see sunshine but this may be an illusion” – I say “there’s sunshine outside”: I interpret what my sensory perception is telling me and come to a conclusion about objective reality out there. I state it as true: “there is sunshine outside” – not as a tentative “in my fallible view” kind of statement.

And I act on these things – I take them as true and I base my actions on that assumption. If my ears tell me that I hear rain outside, and when I look out the window my eyes tell me that it is indeed raining, I reach for my umbrella and open it as I walk out the door. When I am sitting inside the thing which my senses tell me is my car, and I see a red light ahead of me, I put my foot on the brake and stop; when I see a green light ahead of me, I put my foot on the accelerator pedal and drive on. We do this sort of thing all the time, and it is perfectly reasonable behaviour, using the reasonable working assumption that what my senses tell me is very very very probably true.

And yes, it’s reasonable in appropriate contexts to add those extra factors such as: (a) I do X again and again and Y happens every time, therefore I regard it as reasonable to assume that Y always happens when you do X. (b) Someone else did X and observed Y. Several other people did X and observed Y. therefore I regard it as reasonable to assume that Y always happens when you do X.

Those things are reasonable ways of adding extra checks within our system of reliance on sensory perception. But none of this can provide us with 100% certainty, as it’s all dependant on our sensory perception, which can mislead us.

Why am I bothering with this stuff, if I am sane enough to agree that it’s reasonable to rely on our sensory perception in our day to day lives? Am I trying to play with your minds, to make you doubt what you’re seeing and hearing? Am I seeking to make you wonder if the sun really is shining/the rain really is falling/the snow really has snowed? No, I’m not suggesting that you start doubting everything. I just want you to start realising the limitations of those standards by which you seek proof for stuff in general.

I was talking to someone recently about God and as I talked about my conviction that the Bible is true, his reaction kept revolving round the same notion: how can you believe that stuff when you can’t prove it – and the way he wanted it proved was through those good old “reliable” means of observation (through sensory perception) and corroboration. I reminded him that our sensory perception is not infallible and he agreed, but he still kept repeating that demand. Because even though he could see that this method isn’t 100% reliable, he reckons it’s the best we’ve got.

I say it’s a really good method for lots of stuff, but not for everything. I’m not asking anyone to ditch it as a way of finding out if it’s raining outside or for working out the spread of diseases and discovering useful medicine, for instance. I think that’s totally reasonable.

But it isn’t reasonable to use that fallible method to evaluate the truth about God.

That method is good for some things but if you treat it as superior to everything else, and if you use it to evaluate absolutely everything, then there is some truth you will remain blind to. And I believe you’ll be missing out on the most important stuff you need to know.

I will come back and say more another day. Like I said in the previous post, there’s lots to unpack here. (Such as: what do we mean by “truth”? how can we find out this stuff? how can I be certain of the truth about God? Watch this space.)

6 thoughts on “a bit more about that Descartes stuff

  1. I’ve been thinking about this stuff recently, mostly because of the Nye/Hamm debate. One issue that is not addressed in the regular argument comes from believers saying they have a “personal experience” of God. This is something that cannot be tested, or , often, explained. I’ve met many people who explain that belief and faith are good, but getting a personal relationship with God is the key point. And that word “personal” means you can’t explain it, or test it, or pass it on to someone else. It’s just what you’ve experienced with your own senses.

    And that’s fine. You want to have a personal relationship with God, great. You say you know there’s a God because you have personal experience of His presence, then OK. But does that personal, individual knowledge give someone the right to claim that a large slice of experience and research and development is wrong? That the age of the world should be determined by a book, not scientific theory and method? I don’t think so. The problem seems to arise at the point where personal experience and belief gives way to dogma – where what you believe becomes what I SHOULD believe because my view, whatever it is, is wrong because it’s not what you believe. And yes, I’m aware that this is exactly the approach taken by many atheists : believers ought to give up their faith because it’s “wrong”.

    From my perspective, the reason any of this matters is the consequences. To take your example, you throw a rock into the air. If you don’t believe that your past experiments can prove the rock will fall, then stand underneath it. Or let a friend stand underneath it it. They may not be hurt, because it’s only the evidence of your senses that tells you the rock fell before. Maybe it won’t fall for them.

    In America you have people in positions of great power making decisions about the future of energy sources based on the idea that there is someone in the sky looking out for them. Believing the oil won’t run out. Believing that wind is a finite resource and can be slowed by turbines. Believing that science is somehow a dirty word because it conflicts with their personal religious beliefs. As we continue into the future, consuming more, spreading out further, filling the world, it’s invention and scientific endeavour that will allow the people of the world to be fed, to be clothed, to have light and heat. But only if we permit science to advance, allow children to learn the basics and grow in knowledge.

    Jesus said “look at the birds of the air, and the lillies of the field” He encouraged people to trust in God for their food and clothing. I invite anyone with any real faith to give that a go. Except, of course, for the verse that advises against testing God.

    I hope I haven’t come across as disrespectful – tone is so hard to judge in these comment boxes. I like to think I’m reasonable, like you were in your post, but people read these words with the inflection they are handed by their perceptions.

    The short answer is that you have to trust what you have been shown by your senses, because otherwise you would not get out of bed. Like a military battle plan, philosophy rarely survives contact with real life.


    • You don’t come across to me as disrespectful, which is why I’m letting your comment stand. But you seem to be addressing stuff I haven’t talked about, so I’m not going to try and respond – as I said, I’m doing a series of posts, trying to unpack a whole load of different issues, so if you keep reading I expect you’ll see these points addressed.

      I hope you won’t take this the wrong way (as you said, tone is hard to judge in this medium) but when someone starts his comment on my post with references to “the regular argument” and stuff he’s heard believers saying (in general) I feel they’re not engaging with me – I’m not here to answer for what others have said, I’m here to say what I have to say, and am open to discussion of what I have actually said.


      • Fair point, and thank you for letting the “rest” stand in my comment. I always think I’m going to be terribly forensic and incisive, but when it comes to commenting I ramble – apologies! (I also generalise ALL THE TIME! Ha ha ha!)

        If you don’t mind (and time permits) I’d like to come back and try again. But if I don’t, it’s not you, it’s me and my chaos. Thanks for your response.


        • Thank you! and oh, I so very understand about the tendency to ramble – can very much relate :)

          You are very welcome to come back any time. I hope you’ll find time to read the rest of the series as it unfolds. I’m enjoying the process of writing it, and hearing people’s comments can help me sharpen my thinking.


  2. 100% Certainty!?

    Of course we cannot have 100% certainty.

    But we have experienced of how people get hurt and killed because they don’t take it seriously that when they see a car coming toward them at great speed, they have to get out of the car’s path or get hurt and even killed — if they still want to insist that they don’t have 100% certainty.

    So, I see all this discussion about not having 100% certainty to be all foolish and silly.

    Better use your brain to think up ways and means to produce more food for mankind — there you go again, you don’t have 100% certainty that there is hunger or that prices of food can still be lower for everyone to afford.


    • Thank you for taking the trouble to let me know that you think this discussion is foolish :)

      And thank you for reminding me that I never finished writing this series of posts. Maybe it’s time I got back to this, for the sake of those who *are* interested.


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