# What does it mean to "believe" a thing to be true?

post by Bae's Theorem (Senarin) · 2018-12-27T13:28:15.498Z · LW · GW · 13 comments

This is a question post.

answer by ChristianKl · 2018-12-27T23:38:42.777Z · LW(p) · GW(p)

There's no context independent meaning and depending on the context it's useful to use different notions.

I personally distinguish emotional beliefs, probabilistic beliefs and logical beliefs.

The native encoding in which beliefs are stored in minds is emotional and most of the beliefs people hold don't have explicit probabilities attached to them.

When it comes to reasoning about well-defined events in a structured way, probabilities are very helpful.

I'm programming I don't ask myself about the probability that a certain variable might be null. If I consider it a plausible state for the variable to be null, I rather handle it in my code regardless of the probability that I attach to that event.

answer by dumky · 2018-12-27T19:14:52.203Z · LW(p) · GW(p)

That presented with a bet that essentially hinges on that thing being true, you take that bet.

Note that actions involve uncertainty and costs, so they involve a form of informal betting.

comment by ChristianKl · 2018-12-27T23:32:52.145Z · LW(p) · GW(p)

Replies from: Gurkenglas
comment by Gurkenglas · 2018-12-28T12:40:38.418Z · LW(p) · GW(p)

How so? He defined what it means to believe something, as was asked.

Replies from: ChristianKl
comment by ChristianKl · 2018-12-30T14:25:17.202Z · LW(p) · GW(p)

You spoke about what people do as a result of having a belief. That's something separate from talking about what the beliefs are. Or do you think that believes don't exist in minds at all?

Replies from: Gurkenglas
comment by Gurkenglas · 2018-12-30T19:29:41.637Z · LW(p) · GW(p)

You're talking about how human brains represent belief. I'm talking about what functional properties of an intelligence let us identify its beliefs.

answer by G Gordon Worley III · 2018-12-27T19:41:17.098Z · LW(p) · GW(p)

It largely depends on what work you want the words "belief" and "truth" to do.

We might say a belief is a proposition we reason from as if it were true (we'll get back to truth shortly, but I want to screen it off for now). In humans this means a belief is some kind of mental activity corresponding to some statement about the world that is integrated into the mind as part of the network of propositions used in reasoning. Beliefs can exist independent of truth values, though, as anyone who has even mistaken believed one thing and then discovered the world was otherwise knows.

We sometimes use "true belief" to refer to a set of propositions known to be true (known facts) to some entity, so then to believe a thing is true is to know it to be true. This runs into epistemological issues because it necessitates assessing whether something is true, and thus asks us to know the criterion of truth, which runs us headlong into the problem of the criterion. Although I think the problem of the criterion gets at the heart of what you are asking (which is ultimately grounded out in questions of existence), we can be pragmatic here and ignore it by taking a pre-formal leap-of-faith that we know how to asses what is true.

Then to believe a thing is true is simply to know it is how the world is.

answer by Gurkenglas · 2018-12-27T13:58:17.423Z · LW(p) · GW(p)

To use it as an assumption when reasoning about the world. See Making Beliefs Pay Rent (in Anticipated Experiences) [LW · GW].

comment by Bae's Theorem (Senarin) · 2018-12-27T14:44:19.906Z · LW(p) · GW(p)

Just listened to that about 10 minutes ago. Good sequence. When you say "assumption", I hear "a thing that is accepted to be true".

What changes in cognition when something is accepted as true?

Replies from: Gurkenglas, rthomas2
comment by Gurkenglas · 2018-12-28T06:16:37.559Z · LW(p) · GW(p)

I mean that it's used to anticipate experiences, like when you believe that you have a dragon in your garage, expect its breath to keep the house toasty and therefore turn off the heater in advance.

comment by rthomas2 · 2018-12-28T17:20:50.334Z · LW(p) · GW(p)

When something is accepted as true, then observations to the contrary become surprising. So, if I’m surprised to find it raining out, then I’d assumed it was going to be sunny.

answer by Motasaurus · 2019-01-08T00:35:58.997Z · LW(p) · GW(p)

In the Greek πιστεύω ( pisteuó ) is to believe, and is derived from πείθω ( peithó ) , which is to be persuaded of what is true. There are undoubtedly different strengths and types of persuasion, but I find that this understanding (that is to believe something is to be persuaded of the truth of it) is useful in all situations and contexts.