Kuhn: Thoughts on Thought Experiments

The purpose of this essay is to discuss how thought experiments, with regards to Kuhn,

not only aid us in understanding the world but also our conceptual apparatus. I will begin by

giving a brief definition of what a thought experiment is; then proceed to explain their purpose,

how they are able to fulfill it with regards to Kuhn. In the end of the essay, I will exhibit that

thought experiment do aid us in our understanding of the world and our conceptual apparatus by

refuting three different critiques about thought experiments.

Thought experiments are experiments that are simulated within the mind. According to

Kuhn, they are done not only to grasp a better understanding of the world but also of our

conceptual apparatus; they are governed by the rules of how the scientist understands nature

(Kuhn 17). This means that the situations that the scientist creates within the experiment must be

similar to the way he would normally apply his concepts to in the real world (Kuhn 7). The

scientist would not be able to create accurate observations of the real world within his thought

experiment if his thought experiment does not employ to what he is already familiar with. For

example, it would hardly be plausible for a scientist to understand falling bodies within a world

in which gravity does not exist if he has no prior experience in a world in which gravity does not

exist.

There are three things that thought experiments do according to Kuhn. It aids us in

understanding the world, our conceptual apparatus and aid to bring about a paradigm shift. The

primary purpose of a thought experiment is to aid in “the elimination of prior confusion by

forcing the scientist to recognize contradictions that had been inherent in his way of thinking

from the start” (Kuhn 7). If successful, the thought experiment would lead to situations in which

the scientist is forced to revised the way he understands the world. For instance, if a thought

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experiment is created well enough, it can contribute to a paradigm shift as the conceptual view of

the world due to the contradictions that the anomaly that the thought experiment has presented

(Kuhn 52). Kuhn says that “discovery commences with the awareness of anomaly” and the

anomaly is what exhibits the idea that “nature has somehow violated the paradigm-induced

expectations that govern normal science” (Kuhn 52).

Understanding produced by thought experiments are not meant to understand the world,

but rather it aids individuals to learn their concepts and the world together (Kuhn 17). How the

thought experiment teaches the individual about their concepts and the world is by confronting

the scientist with a contradiction or conflict implicit in his mode of thought; the conflicts “arose

not from his mental equipment alone but from difficulties discovered in the attempt to fit the

equipment to previously unassimilated experience” (Kuhn 23). In this passage, Kuhn discusses

how nature plays a role in teaching the individual about the world and his conceptual apparatus.

Due to the paradox that the thought experiment presents him, the scientist unveils a portion of

how nature works with his inability to fit how he views the world with nature actually functions.

The way his conception does not fit shows him that he views the world is not actually how nature

works.

As it was mentioned before, a well created thought experiment can bring about an

anomaly and in turn bring about a crisis within the paradigm (Kuhn 52). This is done by forcing

the scientific community into awareness of the anomalies presented by thought experiment. The

pattern of research of the community changes and one by one the research is turned towards the

anomaly. When attention is turned to the anomaly, the area of the anomaly is explored; this in

turn leads to adjustments within the paradigm. The crisis is “induced by the failure of expectation

and followed by revolution” (Kuhn 25). Only when the adjustment to the new fact, “until the

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scientist has learned to see nature in a different way,” does the paradigm change become

complete (Kuhn 53).

Now, for a thought experiment to be effective “it must, as we have already seen, present a

normal situation which the man who analyzes the experiment feels well equipped by prior

experience to handle” (Kuhn 16). As it was mentioned before, what this means is, in order for a

thought experiment to work, it must first be governed by the rules that the person performing the

experiment is familiar with. If the scientist is to perform a thought experiment otherwise, it

would lead to purely speculative results. For instance, if he was to perform a thought experiment

in a world in which he has no understanding of its nature, then he would not be able to learn

anything as he has no point of reference for the result of the experiment, for example, he would

not know wherein the contradiction lies within the experiment. In Kuhn's words, for the scientist

to learn anything of value from the thought experiment, “the conflict deduced from it must be

one that nature itself could present” (Kuhn 27). The experiment therefore, depends upon the prior

experience of nature (Kuhn 17).

There are three example within the essay A Function for Though Experiments, that Kuhn

uses to show us how conceptual reform and a new understanding of the world due to thought

experiments manifests itself. The first example that Kuhn presents is Piaget's laboratory

experiment. In this experiment, the children are asked to answer which car they think is faster

and how they know that the car that they picked is the faster one. The point of the experiment is

to get the children to learn by showing a contradiction within their perception of the world. At

the beginning of the experiment, the subjects based their decisions on which car is faster by

which car arrived at the finish line first; Kuhn calls this as goal-reaching criterion, which is bases

the notion of faster on the which car reaches the finish line first (Kuhn 9). He tells us that if goal-

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reaching is the only criterion that children use to decide the concept of faster then there is

nothing else that for the children to learn within the experiment (Kuhn 9). But the children, as we

shall see in the next example, employs more than one criterion when trying to convey us their

notion of faster. When they are asked in another experiment, where the red car started later than

the blue and had to move more rapidly to catch up, which car is faster, the respond would have

the red car as the answer. When asked why, the children would respond that they saw it move a

lot quicker than the blue; Kuhn calls this as the perceptual blurriness criterion, which is bases the

notion on faster on the object's movement. So, based on both goal-reaching and perceptual

blurriness criterion, we can conclude that the children were able to learn an adult's conception of

what 'faster' is within Piaget's laboratory (Kuhn 9). Kuhn points out that the the example is meant

to show how learning would work if people are put into certain situations and how they become

aware of the contradictions within situations. For the experiment to be worth anything, as it was

mentioned earlier, the situation presented to the individual must be relevant –it must exhibit cues

in which the subject would usually employ (Kuhn 10).

The second example that Kuhn uses to show us how thought experiments work and how

they can aid us in understanding the world and our conceptual apparatus is Aristotle's paradox of

motion (Kuhn 13). The experiment is set up with two bodies on top of an incline. One would

travel perpendicularly along the height of the incline, while the other would travel along the

frictionless slope. Galileo asks the participants to suppose that if the two bodies were to start

from a similar rest point, then they would acquire a similar terminal velocity and mean speed

when they reach the bottom. When the two bodies are dropped and reach bottom, the participants

are asked which of the two is faster. The experiment creates a situation in which the participants

have to pick a certain concept of speed when deciding if the motion along the perpendicular is

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faster, equal or slower than the motion along the incline (Kuhn 15). The purpose of the

experiment is to create a paradox and lead the participants into state in where they can start a

conceptual reform.

The last example that will be touched upon is the scenario of a scientist living within a

world of uniform speed (Kuhn 18). Within this example, Kuhn stresses the fact that “from

thought experiments most people learn about their concepts and the world together” (Kuhn 17).

He argues that just because thought experiments rely only on data that we already know, does

not mean that there is nothing that thought experiments can teach. When the individuals run the

thought experiment they are the ones that “runs the risk of self-contradiction”, ergo, they will

learn something new about their conceptual world and the nature of the world that experiment

reflects (Kuhn 18). In order to full understand what he means, he tells us to imagine a world

where motions all occur at uniform speed. Kuhn says that if we were to find a scientist within

this world and that scientist consistently employed his concept of physics, then there is nothing

wrong with his science or logic; the scientist has embodied within his concept of speed that only

uniform motion occurs within his world thus his “concept functioned in part as a law of nature”

(Kuhn 18). What Kuhn is trying to show in the prior example is that, since the the concept of the

scientist functioned as a part of the law of nature, it would be difficult for him to recognize the

contradictions within his concept. So this is the area where the thought experiment becomes

useful. What I mean is that if the thought experiment brought the scientist to the awareness of an

existing paradox due to his conceptual scheme then a conceptual change within the scientist and

his understanding of the world would occur as how he thinks about the world would no longer be

consistent.

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There are many arguments against the effectiveness of thought experiments, but for the

sake of brevity I shall present three criticisms. The arguments will be broken in three separate

parts and they are from Michael Bishop, Alisa Bokulich and Ian Hacking.

The first argument I shall present is Bishop's critique. In the essay Why Thought

Experiments Are Not Arguments, Bishop argues that “thought experiments are not arguments”

(Bishop 534). By stating that thought experiments are not arguments, Bishop is claiming that it

would be difficult for us to postulate any type of knowledge coming from thought experiments

(Bishop 535). His reasoning behind claim is, “since we have two different arguments but only

just one thought experiment, the thought experiment cannot be the arguments” (Bishop 534). To

make his point clear Bishop uses the Clock-in-the-Box thought experiment by Bohr and Einstein

to illustrate his idea. It is important to note that we should put most of our attention to how the

scientists arrived to their conclusions, now on to the experiment (Bishop 538). The thought

experiment originates from Werner Heisenberg's uncertainty principle. The principle declares

that “there is an irreducible limit to the accuracy to which pair of conjugate variables (variable

pairs like position position-momentum, and energy-time) can be measured” (Bishop 535). In a

1930 conference, Einstein presented Bohr with a clock-in-the-box thought experiment. The

thought experiment consists of weighing a box full of photons during two intervals; before a

single photon is fired out from a shutter mechanism that opens and after the single photon is fired

out from the shutter mechanism. Using Einstein's theory equation of E = MC2, the photon's

energy can be determined and in turn measure its time of passage to any arbitrary degree of

accuracy. Therefore, based on this thought experiment Einstein concludes that the Heisenberg's

uncertainty principle is false (Bishop 536). But the next day, Bohr showed that there is a

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fundamental limit to the measurement of the the photon's weight (which entails also the energy)

at a particular time using any clock-in-the-box apparatus. According to Bohr, “there is an

irreducible limit to the accuracy to which conjugate variables time and energy can be measured”,

hence the clock-in-the-box thought experiment failed. It could not show that at at particular time

the photon's energy could be measured within any arbitrary degree of accuracy (Bishop 538).

Because of Bohr's argument Einstein abandoned his attempt to undermine the uncertainty

principle.

According to Bishop, the problem lies with both Einstein and Bohr analyzing one thought

experiment and proposing two different arguments (Bishop 538). There are two arguments that

stem from the presented problem and only one can be true. The first is the arguments that were

put forth by both scientists were type-identical (wherein they are talking a similar experiment,

but present it in a different way). Bishop argues that the problem with the first argument is that

the account of the clock-in-the-box episode seriously misrepresented what happened (Bishop

540). And the second is that the thought experiments proposed by Bohr and Einstein were

different tokens (wherein they are not even talking about the same experiment). Bishop's

reasoning behind the second claim is that if Bohr did not replicate the clock-in-the-box thought

experiment, then the thought experiment was not done properly. Since the thought experiment

convinced Einstein and the scientific community then Bohr had repeated the thought experiment,

thus the thought experiment is not type-identical to Einstein's thought experiment (Bishop 540).

In the end, Bishop concludes that “since we have two different arguments but just one thought

experiment, the thought experiment cannot be the arguments” (Bishop 540).

The reason I am presenting Bishop's argument is because he argues that we cannot claim

knowledge from thought experiments as one thought experiment could postulate different types

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of arguments, wherein the individuals involved are no longer speaking about a similar

experiment. I am saying that through the existence of the different interpretations of thought

experiments we learn something about the conceptual apparatus which the scientist used to

analyze the problem presented by the thought experiment; either way, the thought experiment

revealed something about the natural law and also how the scientist views the world, hence it did

its purpose. For example, in the clock-in-the-box thought experiment, Einstein conceptualized

the world with respect to special relativity in an attempt to undermine the uncertainty principle,

but through general relativity Bohr was able to show Einstein's error. Through Bohr's refutation

with the use of the thought experiment, Einstein was able to understand where he erred and how

the natural world worked differently from the way he first conceptualized it to be.

The second argument is from Alisa Bokulich's Rethinking Thought Experiments.

Bokulich argues that some thought experiments are more like ordinary experiments, but when it

comes to function the continuity (thought experiments like ordinary experiments both in a sense

use a similar methodology) between thought experiments and ordinary experiments breakdown.

(Bokulich 286). According to Bokulich, the reason for the breakdown is as follows:

An examination of two thought experiments in contemporary physics reveals that the

same thought experiment can be reanalyzed from the perspective different and incompatible

theories. This fact undermines those accounts of thought experiments that claim their

justificatory power comes from their ability to reveal the laws of nature... I conclude that, while

their interpretation presupposes a whole set of background theories and putative laws, thought

experiments nonetheless can evolve and be retooled for different theories and ends. (Bokulich

285)

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The first example she uses to prove her point is the thought experiment Rockets and Thread. The

experiment involves two rockets firing their engines simultaneously and gently accelerate

relativistically in the same direction, one following the other, with a thread connecting them.

When the rockets reach a four-fifths of light speed they stop accelerating simultaneously and in

move in uniform velocity. To an observer at rest, the two rockets “have been moving in tandem

and are still 100 meters apart”; the question it presents is whether the thread between the rockets

break or not (Bokulich 290). According to Bokulich, there are two ways to approach the

problem: Einstein's special theory of relativity and Lorentz's ether theory.

From the perspective of the special theory of relativity, the thread breaks because it is

Lorentz-contracted (to 60 meters) and can no longer span 100 meters between the rockets. The

theory says that at initial separation the distance between the rockets is only 60 meters, but due to

relativity between the rockets, they do not accelerate and come to rest simultaneously and hence

grow from 60 meters to 166.67 meters. Since the rest frame is 100 meters, the thread breaks as it

cannot reach 166.67 meters between the rockets (Bokulich 291).

On a similar note, special relativity theory's rival the Lorentz's ether theory gives the

same result. According to the theory, motion is relative to a stationary ether frame. The ether is

the medium in which electromagnetic forces are propagated, this is also where molecular forces

are transmitted. Since the rope is made up of atoms (a nuclei with circular orbiting electrons),

once the nuclei begin to move relative to the stationary ether, the orbit of the electrons become

ellipses and contract to the direction of the motion. It is postulated that as the atoms and the

molecules contract so will the rope, and if the thread is not strong enough to overcome the inertia

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of the rockets in an attempt to bring them together as it contracts, the thread will break (Bokulich

292).

She argues that even though both theories agree on the thread breaking, the fact is that

they differ on the perspective on why it occurs and the explanation behind it; therefore, “thought

experiments are no more bound to any one particular theory than ordinary physical experiments

are, and second, they can underdetermine theory choice in the same way too” (Bokulich 293).

Bokulich is saying that thought experiments cannot reveal any laws of nature or the scientist's

conceptual apparatus due to thought experiments being malleable enough to be reanalyzed from

different perspectives; because of the its ability to “underdetermine (account for) theory choice”,

thought experiments undermines any usefulness we can get from it (she is pretty much saying

that it suits the needs of the theory that is being presented, ergo its pointless to use it). But if we

take a look at both the experiments again, it can be inferred that it does teach us something about

nature even though their approach at the two experiments are different. The fact that the two

experiments have corresponding results means that they are grasping an underlying concept

which unites the two theories (for instance, how relativity between objects can lead to break).

Thus, the contrast between the approaches of special relativity and ether theory to solve the

rockets and thread thought experiment exhibits that there is a law there, even though it is not

quite clear to what it is other than the fact that it exists.

The second example that Bokulich presents us is the Einstein-Podolsky-Rosen (EPR)

thought experiment; it is an example of “a thought experiment that has changed and been

modified over time” (Bokulich 293). EPR is a thought experiment that tries to show that

quantum mechanics is incomplete through the paradox “a particle can simultaneously have a

definite position and a definite momentum” (Bokulich 294). According to Bokulich, even though

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EPR presented the paradox, it was not necessarily right. There is evidence that Einstein disagreed

with Podolsky and it was in fact he thought that the thought experiment showed that EPR could

not maintain both states, hence quantum mechanics is complete (Bokulich 293). Even though

EPR gave a solution, the disagreement between Einstein and Podolsky's interpretation shows the

inconsistency that thought experiments presents as did the other interpretations of the thought

experiment in history(Bokulich 293). Bokulich argues that if we take a look at the history of

discussion of the EPR thought experiment, there many oversimplifications which led to the

misunderstanding of the thought experiment; therefore, what we should take from it is that

thought experiments succeeds or fails depending on the “reference to the intentions of the

proponent of the thought experiment” and that they can be “rethought and retooled for new

purposes” (Bokulich 298). She says that it is “the fact that the same thought experiment can be

rethought from the perspective of different and incompatible theories” is what makes the

argument that thought experiments aid us in understanding nature less plausible (Bokulich 299).

Before I argue against what Bokulich said, I will summarize her claim. She argues that,

because thought experiments can be reanalyzed from different perspectives and incompatible

theories, then it cannot reveal the laws of nature. Her main point is because thought experiments

can be molded to fit the needs of the individual interpreting it, it does not produce any

understanding of nature as the individual would just be manipulating it to suit his needs. I will

now argue what Bokulich stated. Just because the thought experiment can be molded into

whatever a theory needs does not mean that it will be consistent with natural law. In more

Kuhnian terms, “our subjects hand in their transactions with nature, successfully employed a

conceptual fabric different from the one ourselves. That fabric was time tested; it had not yet

confronted them with difficulties. Nevertheless, as of the time we encountered them, they had at

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least acquired a variety of experience which could not be assimilated by their traditional mode of

dealing with the world” (Kuhn 26). But in a simpler term, sooner or later, a well thought up

thought experiment will challenge the theory. And if the theory is sound and parallel to the laws

of nature then it will hold, if not, then a paradox will surface and proceed to remodel the

conceptual apparatus and teach the law of nature to the individual employing the theory.

The last criticism I shall entertain is Ian Hacking's argument that thought experiments “do

not have a life on their own” (Hacking 302). Hacking tells us that for an experiment to be

effective, it must have a life on their own. What he means by experiments having a life on their

own is, experiment are organic and they develop and change while at the same time “retain a

certain long-term development which makes us talk about repeating and replicating” them

(Hacking 307). Hacking argues that since thought experiments do not have a life on their own,

then thought experiments are not effective. The reasoning behind the argument is that due to the

nature of thought experiments being fixed and largely immutable, it would be hard for it to

evolve and be used “over and over in new context” (Hacking 307). Thought experiments only

have one tension to expose, Hacking argues, thus they are stuck as they can only “reveal tensions

between one vision of the world and another” (Hacking 307). A thought experiment can only

present one thing to the scientist, the same idea that it presented to the scientist that did the

thought experiment before him; so when people rethink the experiment from different

generations the same idea is being portrayed hence the uselessness of being an experiment

(Hacking 307).

The reason I am presenting Hacking is because of his argument that since thought

experiments are not alive, and by being alive, he means thought experiments are not organic in a

way that they do not present anything new, develop and change as they are always the same, like

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the Aristotle's uniform motion, then it is not useful. Hacking is saying that since thought

experiments are not useful, they would not aid in changing our conceptual apparatus and reveal

the the natural world. He argues that they are used over and over again but there is nothing new

to be obtained from them. Claiming that thought experiments stagnate and do not develop or

change is where I find Hacking errs. According to Bokulich, thought experiments do not

stagnate, but rather they change and become misconstrued; evidence for this is the numerous

interpretation of EPR throughout history (Bokulich 298). The numerous interpretations and ways

to present thought experiments is what Bokulich presents to be the problem with thought

experiments. So now, if we follow Bokulich's argument that thought experiments are always

changing depending on the person interpreting, then we can suppose that they are alive by

Hacking's terms, and if they are alive then it would mean that they would be useful and thus

present us with a new conceptual apparatus and an understanding of the world.

I agree with Kuhn with regards to thought experiments aiding us in understanding nature

and learning about our conceptual apparatus; it is a tool to be used in order to further our

understanding. In the essay above, I have outlined how it is possible for thought experiments to

aid us in learning our conception of nature and understanding the world; through contradictions

of the subject's view of nature and the inability of it to fit into the natural world. But unless the

conflict, which is presented by the thought experiment, has been encountered before by the

subject unclearly, then he cannot learn anything from the thought experiment (Kuhn 27).

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Works Cited

Bishop, Michael. “Why Thought Experiments Are Not Arguments.” Philosophy of Science 66.4

(1999): 534-541.

Bokulich, Alisa. “Rethinking Thought Experiments.” Perspective on Science 9.3 (2001): 285-

307.

Hacking, Ian. “Do Thought Experiments Have a Life of Their Own? Comments on James

Brown, Nancy Nersessian and David Gooding.” Preceedings of the Biennial Meeting of

the Philosophy of Science Association 1992.2 (1992): 302-308.

Kuhn, T. S. “A Function for Thought Experiments.” Scientific Revolutions. Ed. Ian Hacking.

New York: Oxford University Press, 1984. 6-27.

Kuhn, Thomas S. The Structure of Scientific Revolutions 3 rd Edition . Chicago, IL: The

University of Chicago Press, 1996.

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