Appeal to Unknown

A short note on fallacies. It turns out that it is often hard to say what is wrong with certain fallacies, or why we should endeavor to avoid them. Consider what you think is wrong with begging the question. Arguments that beg the question are by definition valid (if the premises are true the conclusion must also be true), and in some cases even sound (provided the premises are true). But still, they seem to be bad qua arguments or perhaps even as ways of reasoning. Unfortunately, it's quite difficult to get a precise handle on the nature of the badness. Some suspect that it has something to do with making knowledge or justified belief, too easy to come by--but even this is up for debate (see the problem of easy knowledge or epistemic bootstrapping which afflicts basically any theory of knowledge and justification under the sun). Similarly, it's really tricky to figure out why we ought to (rationally) follow the rules of valid inference in logic (i.e., ask yourself what it is that justifies you in accepting that modus ponens is a rule you ought to adhere to in forming/evaluating arguments?) and it's hard to figure out just why a rational person ought to avoid fallacies (even though I think we absolutely should).

For the moment, I want to focus my attention on the fallacy dubbed by Gangadeanians as an "appeal to unknown" which is also sometimes called "appeal to ignorance." Let me illustrate with an instance, which admittedly has no hint of creativity. Suppose you are arguing that God does not exist. You present me with the problem of evil as some evidence that God doesn't exist. I then respond, "yeah, but you haven't actually proven that God doesn't exist." If I then further take this fact as proof (or even support) for the proposition that God exists, then this is an appeal to ignorance or unknown.

The bad argument would look like this.

1) There is no successful proof that God doesn't exist.
2) Therefore, God exists. 

Now my point in highlighting this particular fallacy is because I've heard it used against this post of mine. In that piece, I argue that Gangadean's inference from "matter is not eternal" to "therefore, some spirit is eternal" makes a leap. He has set things up on a dichotomy that he has failed to prove (i.e., that existence consists solely of matter and spirit). And I pointed out how since Gangadean is after absolute certainty with respect to all his knowledge claims, and since he claims to know with certainty that God exists, he had better support any and all presuppositions of this inference and thus the dichotomy upon which it rests. In response, some Gangadeanians are too quick to dismiss my argument as an appeal to unknown. But this is plainly wrong. My challengers think I have presented something like the following, but only because they have misunderstood my argument (speaking of fallacies, it's a classic strawman).

1) There is no successful proof that shows that a third substance (non material, non spiritual) does not exist.  

2) Therefore, a third substance exists. 

Indeed this would be a really bad argument--the conclusion simply doesn't follow from the premise. But again this just isn't my argument! Below is what I actually have in mind (expanded in greater detail than I have presented it before).

1) Gangadean presupposes that existence is comprised solely of matter or spirit and no third substance in order to draw the inference that if matter is not eternal, then some spirit must be eternal.  

2) Gangadean hasn't proven that existence is comprised solely of matter or spirit, nor is the claim self-evident/attesting.  

3) Gangadean claims that we cannot know (certainly) things unless they are proven by way of a sound argument or they are self-evident/attesting.   

4) Therefore, we cannot know (certainly) that some spirit must be eternal on the basis of matter being non-eternal. 

Now I'm not conceding that Gangadean has given us a satisfactory account of "self-evident/attesting" or that he has shown the method by which we can determine when something is self-attesting or self-evident. Again, I think ultimately it rests on intuitions. But I'm granting for the sake of argument that there is some real content to the notions and showing how even if there are such things, it doesn't help Gangadean with his broader project. The upshot is that until Gangadean has proven that existence is comprised solely of matter and spirit to begin with, he doesn't actually know (by his own lights) anything that rests on this claim. Thus he doesn't know (again by his own lights) that God exists, even if he has shown that matter is not eternal (also see this post where I question whether he has shown that matter is not eternal).

Finally, it doesn't help the Gangadeanian one bit to respond to me that there doesn't appear to be any positive evidence for the claim that a third substance (immaterial, non spiritual) exists. This is because the lack of evidence for something doesn't prove that that thing fails to exist.