Recently a lot of people I have argued with have brought the following argument against me:
How do you know you are right?
I'd like to post a general answer here, for all to read and ponder. This I will do in the form of a fictional argument between two characters.
Andrew: God exists. God gives people's lives meaning.
Lucy: God does not exist. God is a contradiction and therefore cannot exist in reality.
Andrew: That is just your opinion, it is no less valid than mine.
Lucy: It is not opinion, it is fact, which is valid. Your opinion is invalid.
Andrew: How do you know you are right, and I'm not?
Lucy: Because I have a rational argument to prove I am correct.
Andrew: But how do you know rationality is correct?
Lucy: Because the rational validity of a set of arguments is how well they conform to reality.
Andrew: Whose reality? Yours maybe, but not mine.
Lucy:
1. Reality is objective.
2. Rationality is valid.
3. The rational validity and truth value of a statement is how well it conforms to objective reality.
You accept these three premises implicitly when you engage in rational debate.
1. If reality is not objective then what is there to argue about? and who are arguing with? If reality is all in your mind, then arguing at all makes you irrational, because you would be arguing with yourself; and to do that you must hold two conflicting statements, both of which you completely believe to be true.
2. To claim that rationality is invalid requires the use of rational arguments. You cannot invalidate rationality. To do so would require using rational arguments, and thus require you to first accept rationality is valid. In this sense it is self evident truth; In this sense it is axiomatic.
2a. If rationality were not valid there would be no point in debate. The purpose of debate is to determine truth from falsehood. The validity of rationality presupposes debate. You accept that it is valid in order to debate in the first place.
3. When you argue with someone you accept that arguments can be either correct or incorrect, true or false. If you did not accept this then you'd be in agreement with everything the other said, and there'd be no argument.
But how do you know what 'correct' is? And, further, how do you know you are 'correct' in knowing what 'correct' is? In other words, what is your measure of truth?
If your measure of truth is not objective then why are you arguing? A statement which is 'true' to you may be 'false' to someone else. There could be no debate where 'truth is relative'. You accept that truth is absolute and objective when you begin debating. You accept this because without it there'd be no cause for debate and no purpose in debating.
To argue that truth is relative is to be in contradiction with one's self. You would be arguing, using rational argument, that the [absolute and objective] truth is that: 'the truth is relative'. A solid contradiction. Thus, truth must be objective.
Given that truth is objective, and that rationality is valid, and that reality is objective, how do we know that the rational validity (and truth value) of an argument is how well it conforms to reality?
There are two ways we know this:
1. The first is experimental evidence; The evidence of the senses. If I make a statement: "objects more dense than air fall down". I can objectively test this statement against reality, by dropping objects. I can drop 100 objects and identify that all experimental data points toward this statement being correct. I can assert the statement is correct. I can be certain, because I have all the relevant knowledge, and there is no rational doubt. Certainty of course is not omniscience, but merely a rational standard of confidence based on available knowledge. A standard which is reached by lack of rational doubt and integration and conformity of all relevant facts without contradiction.
2. The second is historical evidence; All knowledge of reality has been discovered through the use of reason, and no valid knowledge has ever been discovered through any other method. The standard by which we separate belief from knowledge is its conformity to reality.
You accept all of the above when you engage in debate, implicitly. To argue against any part, or the whole, is to contradict yourself. In order to debate you must accept these premises:
1. Reality is objective.
2. Rationality is valid.
3. The rational validity and truth value of a statement is how well it conforms to reality.
To debate and not accept these premises is not to debate at all, but rather to irrationally make noise and expect people to respond in a certain way.
Andrew: Hmmpf.
So to answer the question "How do you know you are right?":
"Because I have a valid rational argument, based on valid rational premises, to prove that I am right. And by debating with me, you automatically accept that all valid rational arguments, based on valid rational premises, are correct by the objective measure of absolute truth."
