There is an assumption which is held in regard to argument which I want to discuss, one which is held by almost everyone who argues about anything, from the street to courtroom, classroom to lecturehall, playground to workplace, and everywhere else inbetween. The assumption is held by people of almost every philosophical stripe, from empiricists to intellectualists, objectivists to subjectivists, dogmatists to relativists. This assumption even helps to form the context in which arguments take place, setting expectations of what an argument should achieve and providing standards by which we recognise failure. However, the assumption is also mistaken.
The assumption which I am talking about can be described as follows:
The premises of a good argument provide some reason, support or justification to believe that the argument's conclusion is true.
It is my intent to explain here that according to this definition of a what contitutes a good argument, there are no good arguments. This result is a simple consequence of three commonly understood facts. 1) Invalid arguments provide no justification for their conclusion, 2) Question begging argument provide no justification for their conclusion, and 3) Every valid argument is a question begging argument. In other words, there are no good arguments: the premises of an argument can never provide any reason, support, or justification for the argument's conclusion.
It is commonly noted that a circular argument, though formally valid, does not provide any justification for its conclusion. Instead of 'circular arguments', I think that they are better described as 'equative arguments', because in such an argument the premises and conclusion say the same thing in different ways i.e. the premises and conclusion are equal, and so make an equative argument. In this way we can make a distinction between an equative argument and a deductive argument, where the premises and conclusion are not equal (conventionally, equative arguments form a subset of deductive arguments, but here I am treating them seperately). That said, a deductive argument is not defined solely by the inequality of its premises and conclusion, since the conclusion is also expected to follow validly from the premises i.e. if the premises are true then so must be the conclusion.
There seems to be a general recognition that equative arguments provide no justification for thier conclusion, but there is also a common assumption that deductive arguments can achieve where equative arguments fail. This is mistaken; what makes an argument equative is that both the premises and conclusion share the same logical content i.e. they both have exactly the same logical consequences, and a deductive argument can be distinguished by the fact that the logical content of the conclusion is a proper subset of the logical content of the premises i.e. everything implied by the conclusion is also implied by the premises, but not vice versa. In other words, if you were to lop off the extra logical content of the premises (which is unecessary for the inference) then you would end up with a plain old equative argument.
Think about it like this. If you put some apples into an empty basket then do not expect to pull anything out of that basket except some or all of the apples which you put in. That is how valid arguments work, you put the premises in the basket and then pull nothing out except some or all of the premises which you put in--nothing new is introduced. The trickery to logic is that what we pull out of the basket often looks superficially different to what we put in, but that is just a result of the transformational rules of language, and if we have reasoned correctly then what we put into the basket will provide no justification for what we pull out. In fact, we will just discover new ways to repeat, either wholly or partially, the premises which we started with.
I'm done now, carry on.