Is the simpler explanation is the most likely, the most convincing and the most plausible?

Occam's razor and abduction, on which inference to the best explanation is based, say that the simplest hypothesis is true.

So it turns out that solipsism is the most likely, the most convincing and the most plausible?

Since solipsism has the fewest entities (only my mind) while the existence of other minds requires many entities (all people have minds), it turns out that solipsism is a simpler explanation.

But if we look at the number of explanations that come up, then in solipsism we will have more explanations (a separate explanation of my behavior and a separate explanation for the behavior of other people), while the existence of other minds requires a smaller number of explanations (the same explanation of my behavior and the behavior of others people). So in this case, solipsism is a more complex explanation because it contains more explanations.

So inference to the best explanation, abduction and Occam's razor prove that solipsism is the most likely and the most plausible because it is a simpler hypothesis?

Or is solipsism a more complex hypothesis?

How exactly is simplicity defined in abduction, Occam's razor, and inference to the best explanation?

  • 1
    its a cetirus paribus clause- all things being equal, the simpler hypothesis is preferred (not necessarily true). In the case of solipsism, there is a lack of explanatory power. You are right to think of simplicity- there are multiple ideas of it floating about in the literature
    – emesupap
    Jun 17, 2023 at 2:00
  • Hypothesis are never truth. Not even accepted theories are truth. Science (and knowledge in general) is just a model of the world, not the world itself. Theories model some aspects of reality, never reality in its totality; therefore, no theory is truth (eg. free fall can be described with a formula, but if you measure 100000 free fall events, you will never get the same result -with infinite decimals- as equations predict: science is a model which helps making predictions, but science is not truth).
    – RodolfoAP
    Jun 17, 2023 at 2:20
  • Hypothesis are not true or false, they are just models, like maps, and maps are not the terrain. Your question is if the simplest hypothesis tends to be the most precise model, and that is impossible to know: we can always propose more models. I mean, without an exact number of hypothesis (which might be infinite), you can't calculate any result.
    – RodolfoAP
    Jun 17, 2023 at 7:09
  • How do we determine what type of simplicity we need to apply to a hypothesis when we evaluate it using IBE?
    – Arti
    Jun 17, 2023 at 7:22
  • 2
    Occam's razor and abduction are heuristic rules of thumb that do not prove anything and do not make any final pronouncements on truth. All they do is sieve hypotheses for further inquiry. Picking the "simplest" one first is akin to looking under the streetlight first, which is reasonable, but not because the item is more likely to be there. Solipsism is long past initial stage, so its simplicity is irrelevant. And there is a long list of meanings to "simplicity", with different ones often pointing in different directions, see SEP, Simplicity.
    – Conifold
    Jun 17, 2023 at 12:09

2 Answers 2


In the minimum-description-length formulation of Occam's razor, we are trying to find the shortest computer program (smallest model) that completely and perfectly predicts all the data we're trying to model. Simplicity is simply how many characters (or bits, etc) the model takes to formally describe.

The smallest model that does this is not necessarily the right one, but it is considered more likely than other models, until and unless some new data contradicts it.

Solipsism concerns the universe in general, so the "data we're trying to model" in this case would be all of our observations of the universe.

The first thing to see is that solipsism, by itself, does not completely and perfectly predict all those observations. The most we can say is that solipsism is not incompatible with them - but it is not a complete theory. It makes no predictions at all about what would be observed.

In order to evaluate solipsism in this setting, we need to view it as a possible part of a larger, complete model that does correctly predict all the observations. The question then becomes: does the presence of solipsism in the model help to reduce the length of the model?

To that, I'd say the answer is no. Adding solipsism to your universe-model would only serve to make the model longer and more complex, without adding anything to the model's predictive capabilities.

For an example of what such a model would look like, the model could say that you are a brain-in-a-vat, and the rest of the universe, including every other person, is a computer simulation fed into the brain, not real. Loosely speaking, you could call this a solipsistic universe-model. Such a model needs to include (A) the vat and the brain and how the brain is hooked up to the simulation, and (B) the details of how the simulation works. But, if we compare it to a non-solipsistic universe-model, the non-solipsistic universe-model only needs to include the equivalent of (B), and can omit (A), so it is shorter and simpler.

You might object that this is not really solipsistic because in addition to the self the model also admits to the reality of a vat, wires, and a computer. Granted; it's just to give you an idea. Any solipsistic universe-model would make a separation between the self and the rest of the universe, assigning the status of "real" to the self and "non-real" to the rest of the universe. This is going to add some complexity compared to a universe-model where that separation is absent and the self is modeled with the same code used for the rest of the universe.

  • How do we choose the type of simplicity? In which situation do we judge by the number of entities and in which one by the number of explanations?
    – Arti
    Jun 17, 2023 at 7:20
  • @Arti In the Bayesian minimum-description-length formulation, simplicity is just the length of the model in bits when written down as a computer program, with shorter ones being simpler. But, as mentioned, this is only applicable if the computer program correctly generates all the data under consideration.
    – causative
    Jun 17, 2023 at 16:33

If you have n separate speculations, the probability of each individually being P1, P2 ... Pn, then the probability of them all being true is P1*P2...*Pn, which is always lower than the probability of any subset of the speculations being true. Given that, a theory that requires them all to be true is always less likely than a theory that requires only some of them to be true.

So you might find it help to consider Occam's razor in that light. If you have a theory that depends on n assumptions being true, then finding a way to reduce the number of assumptions can lead to a more likely theory. There is a big 'if' however. Replacing n assumptions of high probability with one assumption will not yield a more likely theory if the probability of the one assumption is sufficiently low.

To put the explanation another way, the more assumptions you build into an explanation, the greater the scope for at least one of them to be wrong.

  • In the solipsism of assumptions more than in the existence of other minds? Because two mechanisms of behavior need to be explained.
    – Arti
    Jun 18, 2023 at 7:58
  • Sorry, I don't understand your comment. Can you please clarify it. Jun 18, 2023 at 8:11
  • Solipsism by itself doesn't explain anything. If you think that yours is the only mind in existence, then how do you explain everything around you in the world? How do you explain the fact that I am answering your question? How do you explain the TV programmes you watch? How do you explain the existence of the food you eat? You need a theory of solipsism that explains all of those things. And you will find that your theory of solipsism cannot be so simple if it is to explain the world around you. Jun 18, 2023 at 8:16
  • That's what I'm saying for it. Solipsism has fewer entities (only one mind) but many explanations and assumptions. The existence of other minds has more essences (many minds), but fewer explanations and assumptions. Which of these two worldviews is simpler? Who decides which assumption is simpler? Is it an individual choice? Thank you
    – Arti
    Jun 18, 2023 at 9:10
  • You are trivialising a complicated question. You cannot say that theory A is better than theory B simply because it assumes fewer entities. Occam's razor can only be brought to bear when other things are equal. If you have two theories that explain the world equally well, the one that makes fewer assumptions is more likely to be right. If one theory is nonsense, it is not more likely to be right just because it makes fewer assumptions. The quality of the assumptions matters too. Jun 18, 2023 at 11:37

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