The first thing the presuppositionalist will do is question how do you know anything with out some absolute standard of logic, such as God. They will in fact wait patiently to refer to something as proven and then leap in, with how do you know? They will say the concept of proof depends on God and yadda yadda. Since this is a stupid question on their part it is tempting to dismiss it as a stupid question and try to explain your evidence. This is a mistake, they will continue to repeat how do you know? indefinitely unless challenged on it. Note that they will still continue to repeat it if challenged, but you can then point out how stupid they are. The best response is to pretend they have asked a serious but simple question and then answer it succinctly. This is my response. It is not original to me in any sense. These are well established axioms but they are effective. These particular axioms are my variation of a set I read on the Skeptical Studies blog. They are largely a simpler paraphrase of those. The presupp won't accept them of course. Their missionary philosophy prevents them from allowing any common ground with atheists. However you will now be able to respond to their "how do you know?" by refering back to these axioms.
Step 1. Perception exists. If I were presented evidence otherwise, I would have to perceive the evidence thereby proving the existence of perception.
Step 2. Consciousness exists, perception requires consciousness therefore consciousness not existing would contradict step 1. However since step 1. is axiomatic consciousness must exist. Also since perception and consciousness are established as discrete entities, solipsism is false because an entity apart from perception is proven to exist.
Step 3. Something exists, proof otherwise would contradict step 2 because step 2 shows that consciousness exists.
Step 4. Multiple things exist, Any disproof would lead to nonseparable identity, i.e. only one identity is. But my TV is black and my chair is not, as given by my sense perceptions. But this is a contradiction. Therefore multiple things must exist. Additionally as it has been established that perception and consciousness are distinct entities, this is further proof that multiple identities exist.
Step 5. Causation exists any proof otherwise would be the result of evidence causing a change in my consciousness, thereby proving causation exists.
Step 6. What our consciousness is aware of through perception is an exact representation of external reality. If this were false it would require that consciousness create perception which is not possible due to Step 1. and 2.
Steps 5 and 6 establish the validity of logic and perception respectively. Having established causation it is therefore possible for though and argumentation to exist. Since logic describes thought and argumentation logic can exist. Step 1 establishes perception as existing, step 6 establishes it as accurate. None of these steps require logic in order to exist, they are self evident. Logic is used to describe them but they are not established through argumentation, they are axiomatic.
It will then be possible to answer most of the presuppos arguments by simply referring to Steps 1-6. They will of course ignore these even if they understand them but will be completely unable to refute them. This will put them on the defensive. Their position can not be established defensively so you can pretty much hold them there forever. However doing so does not refute their position it only prevents them from establishing it, I will continue at a later time with an argument towards refuting their position.
I highly reccomend reading the original article at Skeptical Studies it is far more complete and accurate than these. I have dumbed these down for the benefit of the average TAG advocate. If you wish to get more complex and accurate, the debate at Skeptical Studies is an escellent resource.
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