- Hi, everyone, Jade here. What if I told you that the
observation of a white shoe can support the hypothesis
that all ravens are black? You'd probably think I was
talking complete nonsense, right? And to be fair, that's a
pretty reasonable response. What could a white shoe
possibly have to do with all Ravens being black? Well. This is a video about a phenomenon
called the Raven Paradox. It came about in the early 20th century, when a hopeful group of
scientists and philosophers were trying to understand the world. They called themselves
the Logical Empiricists. And as the name suggests, they thought the only things you needed to understand the world
were logic and empiricism, which is basically
observations of the world we all agree on. In a nutshell, their philosophy was that
any meaningful statement about the world could be
understood by looking at the world. That's the empiricist part. And then we could use
logic to make conclusions. The name the Logical Empiricists gave their way of understanding the world might be familiar to some of you. It's called the scientific method. And as you can imagine, it's greatly influenced the way
that we think about science. But things didn't go as
smoothly as they imagined, as the Raven Paradox
soon flew into the face of their neat little method. Hopefully by the end of this video you'll see that the ways that
we go about doing science, aren't always as straightforward
as you might think. To demonstrate this, let's take inspiration from
the Logical Empiricists and try to do some science
with just logic and empiricism. Imagine you have the hypothesis:
All ravens are black. It seems like a reasonable
hypothesis to make, right? So as a logical empiricist
what kind of steps would you take to
investigate this hypothesis? Well, to gather some empirical evidence, you could go out into the world
and simply find some ravens, check the color of their feathers
and see if they're black. So you do this, and every
raven you find is black. This is good news for your hypothesis. Logical empiricism tells us that with every new black raven you see, you should become more
confident in your hypothesis that all ravens are black. So now that we've gathered
some empirical evidence, it's time to introduce some logic. Basic inference and deduction
tells us that the fact that we've only seen black
ravens support our hypothesis that all ravens are black. We can formalize this logic by saying, observing lots of As with property B supports the hypothesis that all As are B. We can replace A with
raven and B with black, or we can replace them with
anything for that matter. And that logic should still hold. Now we can use the rules of
logic to change this statement in such a way so that it
is logically equivalent. What I mean by logically equivalent is that there could be two sentences that look different on the surface, but are really saying the same thing. For example, the two sentences, "I'll meet you at the cafe at noon." And, "I'll see you at the
shop which sells coffee when the sun is highest in the sky." One might sound a little bit weird, but ultimately they mean the same thing. They're logically equivalent. To make this clearer,
it's often really helpful to draw Venn diagrams to help
visualize what we're saying. Let's draw a circle to
represent all black things, and another disconnected circle to represent all non-black things. Remember our original hypothesis is that all ravens are black, which means that assuming
our hypothesis is true, ravens only exist in the
all-black thing circle. But if we stop and think
about it for a second, we can see that it's logically equivalent to say that there are no
ravens in the non-black circle, or in other words, all
non-black things are not ravens. All ravens are black is
logically equivalent to saying, all non-black things are not ravens. If you're not convinced, take a bit of time to let this sink in, because this should be a
non-controversial statement. Now, can you think of
a non-black non-raven? Well, what about a white shoe? It fits the description. It's not black, it's white. And it's not a raven, it's a shoe. Now let's apply some inductive logic. Take the same formerly
logical statement from before. Observations of A with property
B support the hypothesis that all As are B. We can replace A with non-black things and B with not ravens. So the observation of a white shoe gives support to the statement, all non-black things are not ravens. But hang on a minute, we
showed that the statement, all non-black things are not ravens is logically equivalent to the statement, all ravens are black. So we can swap it in without changing the meaning of the sentence. And what do we get? An observation of a white shoe gives support to the hypothesis
that all ravens are black. Now I don't know about you, but I don't remember the
last time of bird scientist published their results on the
observation of white shoes. And I like to keep up
with my bird science. But all they used to
construct their argument was logic and empiricism. So what went wrong? This is the question
that puzzled philosoph... This is the question that
puzzled philosophers of science for years and still does today. There are many responses to the paradox, but here I'll give the
three most well-known ones. And who knows? They may even inspire you to come up with a theory of your own. One potential response which
our logical empiricist friend, Carl Hempel actually gave, is to just bite the bullet
and say that an observation of a white shoe does help
confirm the hypothesis that all ravens have black. Even if only by a minuscule amount. End of story. The advantage of this response
is that the scientific method stays safely intact and
there is no paradox. But it doesn't really
gel with our intuition of how the world works. Philosopher of science, Nelson Goodman said that if this approach were true, we could do a lot of indoor ornithology. In other words, we could
sit in comfy armchairs and further the study of birds by pointing at colorful objects. Not only that, but if you think about it, an observation of a white shoe also helps confirm the hypothesis
that all ravens are blue or green or purple. Let's see what other options there are. The next response comes
from another famous name in the philosophy of science, Karl Popper. His approach to science can
basically be summed up as, "The job of science and
the scientific method is to show whether or not
a hypothesis is wrong. That's it." This idea of showing something
as false using observation is called falsifiability. And it's what Popper thought was the key feature of
a scientific hypothesis. On the surface, this seems like a reasonable
way of looking at science. It always leaves us
open to the possibility that we might be wrong. But if we look a bit closer,
things get a bit funny. Remember when we said that many
observations of black ravens would support our hypothesis
that all ravens of black? Well, Popper completely
disagreed with this approach. He thought the business of
science was to falsify theories and only falsify them, not make us more confident
in anything being true. An observation of a white shoe wouldn't support the hypothesis
that all ravens are black, but neither would a black raven. To Popper, the notion of
support or confirmation was not the way science should operate. If all we find are black
ravens, all this means is that our hypothesis
is yet to be falsified. This last response, I must tell you is the one I agree with most Just so you know my biases up front. It has to do with the context
surrounding an observation. Let's demonstrate this with some strange but instructive examples. Imagine you have someone
come up to you and say, "Behind my back is a raven. Would you like me to show it to you?" You're a bit creeped out, but as someone interested
in the hypothesis, all ravens of black, you should say yes, since if it's a blue or a purple raven, that would refute your hypothesis. Popper would be proud. Now, imagine someone
comes up to you and says, "Behind my back, I have a black object. Would you like me to show it to you?" You figure the people
here are just a bit weird. So you go to say yes. But if you think about it for a minute, whatever is behind their back could never refute the hypothesis
that all ravens are black. Since even if it is a black raven, not much would be learned
since you knew the object was going to be black
given the circumstance. Finally, a more subtle example. Imagine a third person
comes up to you and says, "Behind my back is a non-black object. Would you like me to show it to you?" Here, you should definitely say yes. Since it could be a blue raven, which could refute your hypothesis. But if this person pulls out a white shoe, in a roundabout way, it gives
support to your hypothesis that all ravens are black. Since given the particular situation, a different outcome could have refuted it. But the crucial point to make here is whether or not we care
about the observation of a white shoe, depends
on the wider context. If this person said they have
a non raven behind their back, then pulling out a white shoe should not matter to you in the slightest, since we only care about ravens. Whereas you should care if they say they have a non-black object since then it has the chance
to be a non black raven. So the takeaway with this response is that sometimes a white shoe does add confidence to your hypothesis, and sometimes it doesn't. You need more information about how the observation was
carried out to make that call. So there are just three theories
about how the Raven Paradox could potentially be resolved. The historical development
after the advent of the logical empiricists
was incredibly fascinating. With its fair share of
heated disagreements and skirmishes between
scientists and philosophers. Some had more radical approaches
to the scientific method, like Paul Feyerabend's total rejection of any kind of universal methodology. Complete scientific anarchy. Other approaches like Bayesian
Analysis were developed and is still being
widely used to this day. But that is a topic for another video. What the Raven Paradox
tells me personally, is that you can't remove science from the specific context
in which it's done, even in principle and
especially in practice. I think this paradox serves
as a really good introduction to the counter-intuitive intricacies of the scientific method. It challenges our assumptions
about how science is done, and in doing so makes us understand it and hopefully appreciate it all the more. But I wanna know what you think. Does the observation of a white
shoe support the hypothesis that all ravens are black? Let me know your thoughts
in the comments below. Being exposed to paradoxes
and brain teasers like this is great for improving
your lateral thinking and training your powers of reasoning. But what's even better is trying to answer
these problems yourself. With today's sponsor,
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premium subscription. I'm doing my first ever live stream to celebrate the channel
reaching 100,000 subscribers. It's going to be on
the 19th of May 8:00 PM Eastern Standard Time. I'll also be reminding you guys
about it on my social media. So make sure to follow
me on there as well. It'd be awesome if you
could make it along. You'll get to see how
awkward I am in real life when I don't have any
prepared lines to say. It's probably gonna be a Q
and A so nothing too exciting. If you have any suggestions of things I can do to make it interesting, please leave them in the comments below. I feel like I need to entertain. Anyway, that's the end of the video. Thanks for watching. Bye. (upbeat music)
