# Dr Johnsons Criteria Dr Johnsons Criteria is a criteria for determining what entities are real and what are not. As explained in [Newtons Force of Gravity Is Not Real, But Einsteins Curvature of Spacetime Is Real](Newtons%20Force%20of%20Gravity%20Is%20Not%20Real,%20But%20Einsteins%20Curvature%20of%20Spacetime%20Is%20Real.md), this criteria is used to refer to [Epistemologically](Epistemology.md) real entities, which in the limit approach [Ontologically](Ontology.md) real entities. It has several different flavors, each of which is interesting in its own right: 1. If something can kick back, it exists. 2. If an entity is [Complex](Complexity.md) and [Autonomous](Autonomous.md) according to our simplest explanation, then that entity is real. 3. If a substantial amount of [Computation](Computation.md) would be required to give us the illusion that a certain entity is real, then that entity is real. ## Vignette > James Boswell relates in his Life of Johnson how he and Dr Johnson were discussing Bishop Berkeley’s solipsistic theory of the non-existence of the material world. Boswell remarked that although no one believed the theory, no one could refute it either. Dr Johnson kicked a large rock and said, as his foot rebounded, ‘I refute it thus.’ Dr Johnson’s point was that Berkeley’s denial of the rock’s existence is [Incompatible](Incompatible.md) with finding an explanation of the rebound that he himself felt. ## Refutation of Solipsism Let's expand on the above, for what is happening is actually quite a deep example of [Problem Driven Epistemology](Problem%20Driven%20Epistemology.md). We have two clashing theories: 1. The theory that the rock does not exist 2. The explanation of the rebounding foot, which argues that the rock does exist These are two [Incompatible](Incompatible.md) ideas - they both cannot be true at the same time. This leaves us with a [Problem](Problem.md). Once we have a problem, we can use the [Problem Solving Process](Problem%20Solving%20Process.md) to address it. Here we wish to determine which explanation, (1) or (2), is preferable. To explain the effect that the rock had on him, Dr Johnson was [Forced To Take a Position](Forced%20To%20Take%20a%20Position.md) on the nature of rocks. Were they part of an autonomous external reality, or were they figments of his imagination? In the latter case he would have to conclude that ‘his imagination’ was itself a vast, complex, autonomous universe. Why exactly was he forced to take a position? [Logical Consistency requires it](Logical%20Consistency%20Forces%20Taking%20a%20Position.md). The same dilemma confronted [the solipsistic professor](Defend%20Science%20by%20Arguing%20Against%20Arbitrary%20Boundaries.md) who, if pressed for explanations, would be [Forced To Take a Position](Forced%20To%20Take%20a%20Position.md) on the nature of the audience. And [the Inquisition](Galileo%20vs%20the%20Inquisition.md) would have been [Forced To Take a Position](Forced%20To%20Take%20a%20Position.md) on the source of the underlying regularity in the motion of planets, a regularity that is explicable only by reference to the heliocentric theory. For all these people, [taking their own position seriously](Take%20Theories%20Seriously%20on%20Their%20Own%20Terms.md) as an explanation of the world would lead them directly to realism and Galilean rationality. We started with a problem: two [Incompatible](Incompatible.md) explanations. We wanted to arrive a [good explanation](We%20Must%20Seek%20Good%20Explanations.md). We were [Forced To Take a Position](Forced%20To%20Take%20a%20Position.md) in order to generate a good explanation. Using methods of criticism (argument) we determined that (2) was the preferable explanation. And just like that we have another [refutation of Solipsism](Defend%20Science%20by%20Arguing%20Against%20Arbitrary%20Boundaries.md). ## Criterion For Reality But this is more than a refutation of [Solipsism](Solipsism.md). This provides us with the [Criterion for Reality](Criterion%20for%20Reality.md) that is used in science: > **Dr Johnsons Criteria**: If something can kick back, it exists. "Kicking back" here simply means that when we "kick" something, the object affects us in ways the require independent explanation. Thus, [Kicking Back Requires an Independent Explanation](Kicking%20Back%20Requires%20an%20Independent%20Explanation.md). For example, Galileo had no means of affecting planets, but he could affect the light that came from them. His equivalent of kicking the rock was refracting that light through the lenses of his telescopes and eyes. That light responded by ‘kicking’ his retina back. The way it kicked back allowed him to conclude not only that the light was real, but that the heliocentric planetary motions required to explain the patterns in which the light arrived were also real. The Inquisition did say that the planets were seen to move [As If](As%20If.md) they and the Earth were in orbit round the Sun, but that in fact they moved round the fixed Earth. But if our goal is to [explain](Explanations.md) the motions of the planets[^1], we must adopt a methodological rule that is something behaves [As If](As%20If.md) it existed, by kicking back and requiring independent explanation, then one regards that as evidence that it does exist. It is this exact reasoning that leads us to classify [Newtons Force of Gravity Is Not Real, But Einsteins Curvature of Spacetime Is Real](Newtons%20Force%20of%20Gravity%20Is%20Not%20Real,%20But%20Einsteins%20Curvature%20of%20Spacetime%20Is%20Real.md). Does that mean that we can use Dr Johnson's criterion to conclude that "planets move as if they are being pushed by angels. Therefore angels exist". No, but only because we have a far superior explanation! The angel theory does not explain why they should push the planets [As If](As%20If.md) their motion were determined by a curvature of space and time, as by the universal laws of [General Relativity](General%20Relativity.md). We have complicated our explanation, general relativity, with worthless baggage concerning angels. We must now explain the angels: how their pushing works, do they ever get tired of pushing, and so on. And *then* we must explain why they push in a way that is identical to that which is described by the theory of general relativity. We could not avoid this question simply by referring to angels; we merely complicated our explanation! So we must remain clear: we regard something as real if it kicks back (requiring an independent explanation) *and that is part of our best explanation.* Notice that it is not how hard something kicks back that forces us to consider it is real. Rather, it its role in the explanation we looking at. Galileo was proposing that the earth was in fact not at rest in the center of the universe, but rotating on it's own axis while hurtling through space as it revolved around the sun. One might first expect that this would provide quite the hard kick. But in fact one of the main methods to observe the "kick" provided by the earths rotation is provided by the subtle motions of a Foucault pendulum. We can start to see that [Complexity](Complexity.md) is particularly relevant in our explanations: * We prefer simpler explanation to more complex ones * We prefer explanations that are capable of accounting for more detail and complexity of phenomena Dr Johnsons Criteria tells us: > We should regard complex entities as real, which if we did not regard them as real would complicate our explanations. For example we should regard the planets as real for if we did not we would be forced into more complicated explanations (e.g. a cosmic planetarium). So the observed complexity in the structure or behavior of an entity is [Necessary but not Sufficient](Necessary%20but%20not%20Sufficient.md) evidence that the entity is real. The entity must also be [Autonomous](Autonomous.md). Consider your reflection in a mirror. Is the person shown *in the mirror* real? Of course not. They have merely borrowed the complexity from your side of the mirror. Given a simple explanation of mirrors, namely that their material properties are such that they reflect whatever light hits them in a highly organized way, we know that nothing that we see in them genuinely lies behind or was created by them. The mirror is not autonomously complex. But wait, what does this say about the [Earth is Enclosed in a Giant Planetarium](Earth%20is%20Enclosed%20in%20a%20Giant%20Planetarium.md) theory? We are still right to reject this theory and regard the planetarium as not real. If we were to regard the planetarium as real, we first need to ask how the planetarium works and *then* how the solar system it displays works. We have only complicated our explanation by introducing this new entity, the planetarium. We could not avoid the later question. Unlike the mirror, we have no explanation of the solar system that the planetarium could easily "reflect" or "borrow", as in the case of the mirror. We can now restate Dr Johnson's criteria as: > **Dr Johnsons Criteria**: If an entity is [Complex](Complexity.md) and [Autonomous](Autonomous.md) according to our simplest (best) explanation, then that entity is real. This notion of complexity leads us straight towards [Complexity Theory](Complexity%20Theory.md). Complexity theory roughly defines a complex process as one that presents us with the result of a substantial [Computation](Computation.md). Consider a planetarium controlled by a computer which calculates the exact image that the projects should display in order to represent the night sky. To do this authentically, the computer has to use the formulae provided by astronomical theories; in fact the computation is identical to the one that it would perform if it were calculating predictions of where an observatory should point its telescopes to see real planets and stars. What we mean by saying that the appearance of the planetarium is ‘as complex’ as that of the night sky it depicts is that those two computations — one describing the night sky, the other describing the planetarium — are largely identical[^2]. It is in this way that the motion of the planets ‘presents us with the results of a substantial computation’ This allows us to yet again restate Dr Johnson's criteria in terms of hypothetical computations: > **Dr Johnsons Criteria**: If a substantial amount of [Computation](Computation.md) would be required to give us the illusion that a certain entity is real, then that entity is real. If Dr Johnson’s leg invariably rebounded when he extended it, then the source of his illusions (e.g. a virtual-reality machine) would need to perform only a simple computation to determine when to give him the rebounding sensation (something like ‘if leg-is-extended then rebound …’). But to reproduce what Dr Johnson experienced in a realistic experiment it would be necessary to take into account where the rock is, whether his foot is going to hit or miss it, and how heavy, how hard and how firmly lodged it is, and whether anyone else has just kicked it out of the way, and so on. This is a vast computation. ## Indispensability Argument Note that Dr Johnsons criterion, and the generation [Criterion for Reality](Criterion%20for%20Reality.md) that David Deutsch has laid out, is a form of [Indispensability Argument](Indispensability%20Argument.md). It is not clear but Deutsch's criterion could have well evolved out of some of the ideas put forth from Quine. See more at [Quine–Putnam indispensability argument - Wikipedia](https://en.wikipedia.org/wiki/Quine%E2%80%93Putnam_indispensability_argument), and Naturalism, Holism[^3]. --- Date: 20241020 Links to: [Fabric of Reality](Fabric%20of%20Reality.md) pg 87 [5 - Reality of Abstractions](5%20-%20Reality%20of%20Abstractions.md) Tags: References: * []() [^1]: We should seek good explanations because that is how we achieve [Progress](Progress.md). This is discussed more in [Problem Driven Epistemology](Problem%20Driven%20Epistemology.md) and [Progress Depends on Knowledge](Progress%20Depends%20on%20Knowledge.md). [^2]: TODO: after finishing chapter 5 summary, describe if the planetarium should be regarded as "real" [^3]: See Chapter 3 of Introduction to the Philosophy of Mathematics, Colyvan (Chapter 3)