What we know about critical thinking
So let us now turn to the particulars of critical thinking. Keep in mind the word: critical. It is no accident this word is related to the word “criticism” - for that is the very technique required in critical thinking. One must criticise. What does this mean? Criticise means what it does to almost all people all of the time with one caveat: it does not carry the emotional liabilities people tend to associate with it. Criticism is a wonderful thing - when applied to ideas. It is the means by which ideas are improved. Criticism is about pointing out what is, or may, be wrong with an idea. It is about highlighting, pointing out, making obvious - the weaknesses, flaws and false assumptions of an idea.
Criticism is a broad topic. In science criticism might, most obviously, consist of an experimental refutation. If the experimental results disagree with the hypothesis - one of three things must hold: the hypothesis is false or the experiment was flawed or both. But this is why we are very careful in science. As careful as we can be. Truly carefully controlled, well performed, accurate and precise experiments can be called “crucial” experiments and can decide between scientific theories. In such a situation, two theories make incompatible predictions about the outcome of an experiment. The experiment is performed and one of the theories is shown to be false. Progress is made. One of those theories is successfully criticised (and typically mortally wounded) in the process. This method of criticism has a simple aim: to show as false an idea. I have written previously about the specifics of how this can work in physics.
This idea of experimental refutation - also called falsification is crucial in science. But it is not the whole story. It is indispensable - but this is only to say it is necessary - but not sufficient. Far from sufficient. Indeed many theories need never actually be tested by an experiment to be refuted scientifically. David Deutsch articulates a great example of this in his excellent book “The Fabric Of Reality” where he asks us to consider the theory that eating a kilogram of grass is a cure for the common cold. That is a testable theory. But do we need to do the experiment to refute it?
No.
So let us be critical in another way of the grass-eating theory. Another eminently scientific way. A wonderfully philosophical way. (I confuse these two words here deliberately to illustrate that here, at the boundary, the techniques really do bridge the permeable wall that separates our rational investigations into the world). If we did actually do the experiment of testing exactly 1kg of grass and find that eating precisely that amount does not cure the cold, this would not show that 1.1kg of grass would not cure the cold. Or 0.9kg. Or any of an infinite number of variations. Although the hypothesis is falsifiable - it is infinitely variable and experiment cannot properly refute all variations of it. Experiment really is not the appropriate critical tool here. So what is?
Explanation. Consider the explanation of how grass cures the cold. Um. What explanation? Right! Do we even have an explanation of how grass might cure the cold? No! If we did we would be able to criticise that. Absent an explanation that is the criticism. For someone who comes along and says “Grass cures the common cold” ask: how? If there is no (reasonable/satisfactory/etc) explanation - it can be rejected. Without an accompanying mechanism of action we can reject it without ever doing the experiment. This is true of almost all claims made in science and elsewhere: we don’t even bother with the experiment. What if it did work? Then we would seek to find out why and until we had a criticism of the theory “eating grass cures colds” that is our best theory that it would be possible to improve (for example, we might find particular amounts work better than others and chemists might isolate the active ingredient. A story much like this explains the theory that chewing on the bark of a willow tree relieves headaches...and that eventually led to pills of aspirin as a really effective headache treatment).
So criticism in science is the way we make progress. It is the means by which we reject false theories. And bad explanations. And no-explanations. This criticism - this critical attitude - is cached out through experiments. But not only experiments as I explain above: it can be knock-down, full stop, over-and-out refutation even without an experiment.
And this is true in all subjects, in all spheres of knowledge, always. Does it work elsewhere?
Criticism is a broad topic. In science criticism might, most obviously, consist of an experimental refutation. If the experimental results disagree with the hypothesis - one of three things must hold: the hypothesis is false or the experiment was flawed or both. But this is why we are very careful in science. As careful as we can be. Truly carefully controlled, well performed, accurate and precise experiments can be called “crucial” experiments and can decide between scientific theories. In such a situation, two theories make incompatible predictions about the outcome of an experiment. The experiment is performed and one of the theories is shown to be false. Progress is made. One of those theories is successfully criticised (and typically mortally wounded) in the process. This method of criticism has a simple aim: to show as false an idea. I have written previously about the specifics of how this can work in physics.
This idea of experimental refutation - also called falsification is crucial in science. But it is not the whole story. It is indispensable - but this is only to say it is necessary - but not sufficient. Far from sufficient. Indeed many theories need never actually be tested by an experiment to be refuted scientifically. David Deutsch articulates a great example of this in his excellent book “The Fabric Of Reality” where he asks us to consider the theory that eating a kilogram of grass is a cure for the common cold. That is a testable theory. But do we need to do the experiment to refute it?
No.
So let us be critical in another way of the grass-eating theory. Another eminently scientific way. A wonderfully philosophical way. (I confuse these two words here deliberately to illustrate that here, at the boundary, the techniques really do bridge the permeable wall that separates our rational investigations into the world). If we did actually do the experiment of testing exactly 1kg of grass and find that eating precisely that amount does not cure the cold, this would not show that 1.1kg of grass would not cure the cold. Or 0.9kg. Or any of an infinite number of variations. Although the hypothesis is falsifiable - it is infinitely variable and experiment cannot properly refute all variations of it. Experiment really is not the appropriate critical tool here. So what is?
Explanation. Consider the explanation of how grass cures the cold. Um. What explanation? Right! Do we even have an explanation of how grass might cure the cold? No! If we did we would be able to criticise that. Absent an explanation that is the criticism. For someone who comes along and says “Grass cures the common cold” ask: how? If there is no (reasonable/satisfactory/etc) explanation - it can be rejected. Without an accompanying mechanism of action we can reject it without ever doing the experiment. This is true of almost all claims made in science and elsewhere: we don’t even bother with the experiment. What if it did work? Then we would seek to find out why and until we had a criticism of the theory “eating grass cures colds” that is our best theory that it would be possible to improve (for example, we might find particular amounts work better than others and chemists might isolate the active ingredient. A story much like this explains the theory that chewing on the bark of a willow tree relieves headaches...and that eventually led to pills of aspirin as a really effective headache treatment).
So criticism in science is the way we make progress. It is the means by which we reject false theories. And bad explanations. And no-explanations. This criticism - this critical attitude - is cached out through experiments. But not only experiments as I explain above: it can be knock-down, full stop, over-and-out refutation even without an experiment.
And this is true in all subjects, in all spheres of knowledge, always. Does it work elsewhere?