Influences on Deutsch
David Deutsch’s main influence is Karl Popper. So much so that Deutsch magnanimously describes his work as footnotes to Popper.
However, there are other thinker’s fingerprints throughout Deutsch's work1.
In Deutsch Eats Rationalism, I discussed how the Deutschian worldview contradicts many tenets of rationalism. Reconciling these problems is a personal project.
I’ve also tried to organize the different areas of disagreement with better hope of reconciling them.
Some of the conflicts comes from Popper’s influence, but some of it comes from elsewhere. So it may be helpful to list out the thinkers who influenced Deutsch.
Karl Popper
Let’s start with the key influence: Karl Popper.
Epistemology
Popper’s influence on Deutsch is mainly in epistemology (the area of philosophy concerned with knowledge). Some specific key Popperian ideas that influenced Deutsch are:
We are fallible.
Induction does not create knowledge.
Knowledge comes from guesses and error correction.
Knowledge is unjustified.
Future knowledge cannot be predicted.
These ideas conflict with core rationalist tenets such as Bayesianism and forecasting. I’ve discussed these ideas (and how they conflict with rationalism) in more detail so I won’t get into the weeds here.
Political philosophy
Deutsch is also influenced by Popper's political philosophy. The key ideas being:
Democracy is about removing rulers peacefully (rather than proportional representation).
Institutions should be changed incrementally.
Popper’s political philosophy stems from his epistemology. We are fallible, knowledge grows via error correction, and there is no ultimate justification. So rather than being concerned with who should rule, (which implies a justified right answer), we should be concerned with setting up institutions to enable error correction.
An archived economist article by Popper nicely summarizes this position.
Let’s start with the key influence: Karl Popper.
Other influences
Although Deutsch's worldview is mainly Popperian, he is influenced by other thinkers too. Sometimes these thinkers came to similar conclusions to Popper. Sometimes their ideas were simply consistent with the Popperian worldview.
Let’s look at the different areas they influenced Deutsch in.
Jacob Bronowski
One of Bronowski’s key ideas is that the human condition is best captured by our reliance on knowledge rather than the environment: We, unlike other animals, can subdue our environment.
The earth is not uniquely suited to human life. Our ability to tame the earth, via knowledge, is what makes it home.
Bronowksi was aware of Popper but did not discuss his ideas at length. Unfortunately, Popper may not have even been aware of Bronowski. Deutsch synthesizes the two thinkers, both naturalized British citizens: Popper describes how knowledge is created. Bronowksi describes some of its impacts.
Deutsch wrote a lovely ode to Bronowski’s documentary series (and accompanying book) The Ascent of Man.
William Godwin
William Godwin is all about freedom. He is against coercion in all forms. For him, we must rely on persuasion.
It is wrong to justify coercion over others based on the idea that you know what’s better for them. As Godwin pointed out, it’s a poor argument for our superior reason if we are unable to make such an obviously correct case understood.
We can connect this anti-coercion position to Popper’s epistemology in a few ways. Firstly, everyone is fallible: we can never be certain that the behaviors we are trying to coerce are right: We might be the baddies. Secondly, knowledge grows via error correction. Preventing others from making criticism via the threat of coercion totally dismantles the very mechanism that knowledge grows. Finally, knowledge grows via guesses. It is an active process of the learner. It cannot be poured into passive minds by force.
Deutsch is against coercion across the board. He even applies this to how we should treat children. Deutsch argues to take them seriously, an extension of Popper’s epistemology. An extension that Godwin anticipated by 130 years.
Alan Turing
Alan Turing is well known as one of the pioneers of the computer. He is father of the Turing machine which bears his name. A thought experiment where a simple machine calculates inputs by manipulating symbols on a roll of tape.
A Turing machine can perform any computable task if it has enough tape (ie enough memory). A computable task is simply anything that is computable. Some things, quite famously, are not computable such as the halting problem.
So anything that is computable is computable by this simple machine.
Computable tasks can all be done by our everyday computers too. Our computers are described as “Turing complete” which means that they can perform any function that a Turing machine can perform.
Deutsch came along and noted that if quantum physics describes reality, then a quantum computer must be able to compute any physical process. We can program physical processes once we’ve understood them.
Alfred Tarski
Deutsch subscribes to Tarski’s notion of truth2. Namely, truth is objective correspondence with facts: A claim is true, if it corresponds with reality. This view implies that objective truth exists.
As we’ve noted, Deutsch is a fallibilist. Although objective truth exists, we can never be certain we have found it.
Hugh Everett
Everett conjectured an explanation for weird results in quantum physics: Multiple universes exist. Deutsch agrees. But takes issue with calling it an interpretation. Rather, it’s the explanation of quantum physics. It’s the best explanation we have. In fact, it’s the only explanation.
Many wince at multiple universes because not only can we not see them, but we can never see them. This is where the connection of Popper comes in: knowledge doesn’t come from induction (generalizing from repeated observations) rather it comes from conjecturing good (ie, hard-to-vary) explanations and then criticizing these explanations with arguments or empircal tests.
Popper explored explanation’s role in science3. Deutsch emphasised it. Simply put: knowledge growth and progress is a quest for good explanations.
Dialling back to quantum physics: Multiple universes are analogous to dinosaurs. Their existence explains the evidence we see around us or in experiments (weird shadow results and fossils respectively). We don’t actually see dinosaurs. We see weird old rocks. The existence of dinosaurs explains the fossils. The existence of multiple universes explains the quantum results.
Space really is curved. Dinosaurs really did roam the earth. Multiple universes really do exist.
Richard Dawkins (& Charles Darwin)
There are three main areas where evolutionary theory has influenced Deutsch’s thought.
The first is that the growth of knowledge, according to Popper, is an evolutionary process. As we’ve noted, knowledge grows via guesses and criticism. Evolution in nature works via random mutations and selection pressure from the environment. This is directly analogous to how knowledge grows. The random mutation of genes is analogous to guesses and selection pressure of whether a gene gets replicated or not is analogous to criticism.
In fact, it’s more than an analogy. The evolutionary process is knowledge growth. Knowledge is instanited in our genes. A bird’s genes contain the knowledge of flight. A fish’s genes contain the knowledge to swim.
Deutsch distinguishes this knowledge from explanatory knowledge. Both are knowledge in terms of causing transformations in the world. However, explanatory knowledge comes from our bold creative guesses. They explain the seen in the terms of the unseen.
The second area is Dawkins’ emphasis on the gene as the unit of selection. The knowledge in genes relate to how to replicate themselves. It is not the survival of the fittest. However, genetic knowledge is often instantied as heuristics that enable organisms carrying genes to survive and reproduce.
This relates to the third area: Dawkins coined the word “meme” to denote an idea that is a replicator. Memes are the mechanism of cultural evolution. Like genes, memes create knowledge to replicate themselves: A population of meme replicators will be taken over by variants that are better than their rivals at causing themselves to be replicated.
Deutsch talks about two strategies of meme replication: static vs dynamic. Static memes rely on being shielded from criticism to survive (ie, dogma). Dynamic memes rely on being useful: it solves a problem, so it is shared.
Deutsch / Unsure
A key idea for Deutsch is that humans are universal explainers. Like other key Deutschian ideas, it’s not obvious at first what this means.
I think it simply means that the universe is explicable by humans. We can create knowledge by making bold guesses. With this knowledge, we can subdue our environment and solve problems.
It’s not just that we have the ability to explain some things, we are universal explainers. Everything, in principle, can be explained. There are no barriers to our understanding. There is no phenomenon that is out of reach.
This is why Deutsch says that all problems are solvable. Solving problems is a matter of knowing how to. There are no barriers to this, so there are no barriers to solving problems.
The idea that we are universal explainers is even more monumental: It is true for all people. All of us can create knowledge in this unlimited sense.
Having an ability to explain the world is discrete: Either you can create explanations or you can’t. If you can create explanations, there are no barriers.
As I’ve discussed, this has profound implications. It seemingly contradicts with evidence in behavioural genetics. Differences among people, including intelligence as measured by IQ, is partly due to genetic differences. However, genetic differences imply a barrier, a genetic barrier to be exact. This would run contra to human universality.
So where does this key Deutschian idea come from? As far as I can tell, it is original to Deutsch.
It might come from Popper’s fallibilism. I can sort of see a connection with fallibilism. Claiming that a problem cannot be solved implies certainty.
Further, people being uninversal, as Deutsch describes them, seems related to Turing’s work on universal computation. Our minds are computers (ie, the computational theory of mind) and computers are universal (ie universal computation). This seems related to describing humans as universal.
It would be useful if Deutsch clarified if Turing’s work on universal computation relates to Deutsch’s claim of human universality.
Popper and Turing aside, Deutsch’s claim of human universality seemingly stems from a simple argument. As I noted in my primer:
Deutsch argues that invoking unknowable knowledge is equivalent to appealing to the supernatural. Both are non-explanations. Such knowledge would resemble Zeus as they would both control us but remain unknowable.
So we have this totally massive claim, that all people can equally create unbounded knowledge, which seemingly contradicts behavioural genetics, evolutionary psychlogy, cognitive biases, and anything that implies some sort of barrier. And it all comse from the simple argument that it’s like saying “God did it”.
Indeed, Deutsch dedicated his first book, The Fabric of Reality, to four of the thinkers listed here: Popper, Everett, Turing, and Dawkins.
See Popper’s Objective Knowledge, pg 199:
What a nice summary. I've forwarded to a friend in the hope we'll discuss it over a glass of wine soon.