How can I know that I know something?


This also a question about what is the definition of knowledge.

Sharon Salmon

Posted 2015-04-24T16:10:02.553

Reputation: 181

Question was closed 2015-04-25T14:06:57.487

possible duplicate of Do we know whether we know something?

– Dave – 2015-04-24T16:54:14.483

On second thought, probably not duplicate; though related. – Dave – 2015-04-24T17:19:21.007

1If you're asking for a definition, this question is off topic per the [help]. Please specify which definition of knowledge you're using, and what research you have done on this topic already. – None – 2015-04-24T18:11:38.530

1Why the down vote? this is a valid question in epistemology. – Alexander S King – 2015-04-24T21:37:31.653

2@AlexanderSKing see Keelan's comment; way too broad without some narrowing context. – Dave – 2015-04-24T22:27:12.007

I'm now voting to close this question as off topic as it's asking for a definition and you did not make an attempt to make the question a better fit for this site. – None – 2015-04-25T11:25:34.413

I don't understand the purpose of this site if everyone is voting to close discussions instead of discussing – Sharon Salmon – 2015-04-25T12:14:29.450

@SharonSalmon - it's not a discussion site. It's a StackExchange (see So it's suited to questions that mirror certain types of programming and technical questions. That means we can answers certain types of questions but not all, and it is not well-suited to open-ended discussions...

– virmaior – 2015-04-25T14:06:51.577



A well known definition of knowledge is the Justified True Belief (JTB) account.

For me to know x, the following necessary conditions must hold:

  • x is true
  • I believe that x
  • I am justified in believing that x

These conditions are individually necessary and jointly sufficient.

However, the JTB account of knowledge can fall prey to the Gettier problem. Here is the classical formulation of the problem:

Smith and Jones have applied for a particular job. Smith has been told by the company president that Jones will win the job. Smith combines this with his observation that there are 10 coins in Jones’ pocket. He then infers that whoever gets the job, will have 10 coins in their pocket. Smith's belief does have a fair amount of justification. He was told by the company president that Jones will win the job & he observed that Jones has 10 coins in his pocket.

However, it turns out that Smith ends up winning the job. He also had 10 coins in his pocket yet he was unaware of this.

Smith’s belief was that the winner would have 10 coins in his pocket, this is true. Smith therefore held a true belief. However, Smith did not know that he had 10 coins in his pocket. As a result of this new information, can we really say that Smith has a JTB?

Just to highlight that there is more than one approach to knowledge, take a look at the following.

I know x if and only if:

  • x is true
  • I believe that x
  • Belief in x is the result of a reliable process

This is a broad picture of an approach to knowledge known as reliabilism. It is concerned with the truth-conduciveness of your belief forming method.

See for further information.

Five σ

Posted 2015-04-24T16:10:02.553

Reputation: 1 118

I don't understand why believing the one that will get the job will have 10 coins is considered true believe ? It can be one of many beliefs and it is just speculation.the winher can have any amount of coins for many reasons.I think Plato should have listen to his teacher Socrates and accept there is ni such thing as knowledge,its an illusion – Sharon Salmon – 2015-04-24T21:32:40.743


This isn't a question with a single, universally endorsed answer, but one with a long history of debate. The field that encompasses study of knowledge is called Epistemology.

One of the most foundational definitions of knowledge, credited to Plato, is that knowledge is "justified, true belief," meaning that you believe something AND the something you believe is true AND you have a good reason for believing it. If you accept this, then you know you know something when you have a justified true belief that you have a justified true belief about something.

This definition has often been challenged, however, see the above link for more info.

Chris Sunami supports Monica

Posted 2015-04-24T16:10:02.553

Reputation: 23 641

How can someone tell objectively that something he believes in is "true" ? – Sharon Salmon – 2015-04-24T18:36:05.263

1@SharonSalmon You could write a whole book, and not even begin to scratch the surface on the debate over answers to that question... You might have better luck if you asked what a specific philosopher said about that question. Otherwise you're just directly tackling one of the central ongoing debates in all philosophy. – Chris Sunami supports Monica – 2015-04-24T18:41:13.577

@SharonSalmon - in order for something to be considered objective it should be repeatable, ie, others can repeat your steps and get the same result. Quantitative measurements are objective. (Posted to wrong place last time). If you want to know if what you know is true, ask others to help test it with you. – MikeHelland – 2015-04-24T21:24:47.437


I think knowledge is a term that is only relevant to mathematical truths where we are the creators of the rules and the axioms. Then we can claim knowledge of things in the scope of this created world. But we cannot do this on our real world because there are no axioms in the real world, only assumptions. Although it is very hard to accept, we don't really know if tomorrow the sun will shine. We only have very strong belief it will, because we have very strong belief in science, but it is just belief and not knowledge. I truly believe that getting used to this can make people much happier just by itself, because it gives a better perspective about the notion of just.

Sharon Salmon

Posted 2015-04-24T16:10:02.553

Reputation: 181


At some point, I believe we should just accept the way we comprehend the world, take it as an axiom, without questioning it. The goal is to find that border that is generally accepted by all of us - you can always continue asking more 'but why' questions with regard to any topic, but we generally assume it's reasonable to stop at some point. Otherwise, you would spend your life on asking such questions which isn't a very efficient way of life.


Posted 2015-04-24T16:10:02.553

Reputation: 473

Sorry but I don't agree with that.I can live perfectly and efficiently by accepting that all I can have is beliefs and not knowledge. – Sharon Salmon – 2015-04-24T21:03:05.887

Yes, I agree with what you've said. It agrees with what I've written though. My point is that the process of asking 'why' questions will never end, so at some point you need to accept the statements you're questioning as true. – user107986 – 2015-04-24T21:05:31.907

So if I say the sun will shone every morning and others repeat my test and see it true,is it true forever ? – Sharon Salmon – 2015-04-24T21:24:51.873

Of course not - there's a a very little chance that the sun will not shine the next morning - but it's possible. – user107986 – 2015-04-24T22:43:17.843

You don't know if the chance is big or small ,you can only assume (i.e. believe) the chance is very small. Saying anything about what will happen tomorrow is future telling and no one can do that.unless god himself came to you and told you that the world obbay the laws of chance and not random,there is no way you "know" what are the chances fo the sun to shine tomorrow – Sharon Salmon – 2015-04-25T07:32:37.970