David Deutsch's essay 'Taking Children Seriously and fallibilism' was first published in 1997 in Taking Children Seriously (TCS) issue 23.

Broadly, the essay is about epistemology – fallibilism, and knowledge in particular. I read it the other night and noticed several things worth criticizing. I suggest you read the essay first, then come back here. Comments on language should be taken with a grain of salt since I'm not a native speaker.

Use of the same word in two opposing contexts

The essay starts with the following sentence:

Over two millennia ago, the idea that human beings are inherently fallible was introduced into the foundations of the theory of knowledge by Pre-Socratic philosophers.

Those familiar with Deutsch's philosophy will know that he agrees with "the idea that human beings are inherently fallible". He thinks it's a good thing that this idea "was introduced into the foundations of the theory of knowledge". Consider his use of the word "foundations" in this context. Notably, he uses the same word at the end of the same paragraph, where he paraphrases a view he disagrees with:

‘You’ve got to build on solid foundations or you’ll never get anywhere’, [defenders of tyranny] claim.

Readers may be confused. They might ask whether Deutsch isn't building on what he considers solid foundations at the beginning of the paragraph and whether he contradicts himself.

I believe he does not contradict himself. He just uses the same word – 'foundation' – in two different senses, which is confusing.

In the first sense, I'm guessing he means "foundations" as in 'important, early aspects'. In the second, he seems to mean it as in 'aspects forever secure and beyond criticism'. To avoid confusion, one could use different words – for example, one could say 'fundamentals' for the agreeable case. Or one could leave that part out and simply say 'was introduced into the theory of knowledge'.

Justification

Deutsch begins the essay by criticizing attempts to justify theories – he's one of the people who deny "the possibility of [...] justified knowledge". So it may confuse the reader that later on he speaks of "reasons" that "the theory of Taking Children Seriously" is true. He also writes (emphasis added):

[N]on-coercive educational theory is consistent with wider philosophical ideas [...] that we hold for independent reasons.

I think Deutsch just means to argue for TCS, and that TCS is compatible with other, independent ideas that follow from (can be deduced from) ideas that are non-controversial in this problem situation. He invokes Popper's concept of background knowledge, of which these independent ideas are a part, and which, by definition, is non-controversial. It cannot refute TCS since it is compatible with TCS.

A bit further down, he uses the same logic to show how one might criticize TCS instead:

[Argument and criticism] might show that [TCS] contradicts some principles that we have independent reasons to retain.

In other words, if TCS conflicted with something derived from background knowledge, we'd discard TCS.

We find the explanation for this valid use of justification in Popper's Objective Knowledge.¹ As I commented here on a related post, on p. 67, Popper speaks of "the logical justification of the preference for one theory over another" (emphasis removed) and calls it "the only kind of ‘justification’ which I believe possible […]".

It would have been helpful if Deutsch had explained to the reader why it's okay to justify TCS in this case but not in other cases and why.

Spelling and grammar

Pre-Socratic philosophers

Deutsch potentially spelled "Pre-Socratic" wrong. Apparently it's spelled with a lowercase 'p': 'pre-Socratic'

We believe that it possible [...].

The word 'is' is missing.

favorite theory

Deutsch is British. Why is "favorite" not spelled 'favourite'? Maybe an American copy editor changed the spelling before publication? If so, there is an inconsistency: later on, Deutsch writes "criticise" instead of 'criticize'.

[W]hat passes for rival educational theories all depend on [...].

It should say 'depends' (singular). This mistake strikes me as an instance of the wrong-number pattern, and I have written more about this particular instance here.

Experiment could not refute the theory of Taking Children Seriously, but argument and criticism might. For instance, it might [...].

It should say 'they might' instead of "it might" since that part refers to "argument and criticism". Same in the next sentence, which starts with "Or it might show" and so on.

There is often a moment of understanding, when you assimilate an explanation of why [...].

Grammarly says there should be no comma after "understanding".

Style

But because we are fallible, it is not possible for us to know which of the ideas that we believe to be true are in fact true, [...].

Grammarly says the part "it is not possible for us to know" is unnecessarily wordy. One could simply say 'we cannot possibly know'.

in fact

Toward the end of the second paragraph, Deutsch uses the phrase "in fact" three times in three subsequent sentences. That's repetitive.

Missing credit

[W]e do believe that our successive theories can become objectively truer – with more true implications and fewer errors.

This sounds like a vague summary of Karl Popper's idea of verisimilitude (or truthlikeness), see e.g. Objective Knowledge p. 52 ff.

Deutsch's criticism of justified/certain knowledge rests on Popper's, which in turn rests on David Hume's, see e.g. Objective Knowledge p. 3 f. and p. 7 (more on that below).

Deutsch got the idea that "it is not possible for us to know which of the ideas that we believe to be true are in fact true" from Popper, e.g. in Objective Knowledge p. 55:

Every unambiguous statement is true or false (although we may not know whether it is the one or the other); [...].

Popper in turn got this from Xenophanes, whom he quotes in his Conjectures and Refutations² p. 34:

And even if by chance he were to utter
The perfect truth, he would himself not know it;
For all is but a woven web of guesses.

In his book The Beginning of Infinity, Deutsch (mis)quotes this passage from Popper's The World of Parmenides.

The idea that experimental testing "cannot prove that any theory is true, because it may yet make many false predictions in some [...] other situations" is Hume's. Popper credits Hume in Objective Knowledge p. 7 (I'm leaving out a footnote marker at the end of the quote):

I formulate Hume’s logical problem of induction as follows:
L₁ Can the claim that an explanatory universal theory is true be justified by ‘empirical reasons’; that is, by assuming the truth of certain test statements or observation statements (which, it may be said, are ‘based on experience’)?
My answer to the problem is the same as Hume’s [emphasis added]: No, it cannot; no number of true test statements would justify the claim that an explanatory universal theory is true.

Note however that, unlike Deutsch, Popper does not say this about any theory, but only about "explanatory universal" ones.

Popper also writes in The Logic of Scientific Discovery³ p. 10:

[Experimental testing] can only temporarily support [a] theory, for subsequent negative decisions may always overthrow it.

The idea that bad epistemology is "a recipe for tyranny" is Popper's. For example, in Conjectures and Refutations p. 11, he criticizes the manifest-truth error, which is one particular kind of bad epistemology:

The theory that truth is manifest—that it is there for everyone to see, if only he wants to see it—this theory is the basis of almost every kind of fanaticism. For only the most depraved wickedness can refuse to see the manifest truth; […].

See also this video where Popper explains how different epistemologies can lead to different politics and how that can go wrong.

To be sure, Deutsch mentions Popper by name, but he does not directly associate Popper with these ideas, so the reader may easily miss that Popper came up with them.

Conclusion

The essay contains highly relevant ideas, but it seems like Deutsch wrote it a bit carelessly. Some of the borrowed ideas are of lower quality than the originals and have fewer details than in the sources. That would be fine since the essay is on the shorter side, but exact sources should be given so that readers can learn more. I have noticed a similar reduction in quality of some borrowed ideas in Deutsch's book The Beginning of Infinity – see the "Missing credit" section here.