You can either provide a rebutting defeater for a premise, or you can provide an undercutting defeater for a premise.
A rebutting defeater is:
- Showing that the premise is false (or likely false), thereby refuting it
An undercutting defeater is:
- Undercutting the justification one has for accepting a premise as true
- You can show one or more of the following:
- The justification is unknowable
- The justification does not adequately support the premise
- The premise is merely an unsupported assumption
- The justification for the premise relies on the truth of the conclusion of the argument (or the truth of the premise that is being questioned)
- An undercutting defeater essentially pulls the rug from under the argument
With these definitions out of the way, let’s dig into two more ways to critically assess arguments!
(1) One or more premises has a justification that is undercut by some consideration. This means that we should not accept the premise on the basis of the provided justification.
Some atheists will claim that there are instances of intense suffering that an omnipotent, omniscient, wholly good being could prevent without thereby losing some greater good or preventing some evil equally bad or worse. One justification commonly leveled in support of this claim is as follows. One looks at the world, finds a token or type of evil state of affairs, and then argues that because we cannot conceive of a justifying reason for this evil to occur, there is no justification (else: there is probably no such justification). The atheist would call such evil gratuitous (pointless, unnecessary, unwarranted, unjustified) evil.
Skeptical theism provides an excellent example of the type of undercutting defeater described in (1). Skeptical theism aims to undercut the atheist’s inference from “I do not see any justifying reason” to “therefore, there (probably) is no justifying reason”. But this noseeum inference can only be justified under certain conditions. Take, for instance, the example of a doctor dropping a needle on the floor, picking up the needle, and proclaiming, “I do not see any germs on the needle, and hence there (probably) are no germs.” This is a poor noseeum inference, because if there were germs, then we would not expect to see them. In fact, if there were germs present, we would positively expect not to see them!
Another example of a noseeum inference is as follows. If you walk into your living room and see no elephant, you can justifiably say “I see no elephant in the room, therefore (probably) there is no elephant in the room”. However, you cannot justifiably infer that, “I see no dust in the room, therefore (probably) there is no dust in the room”. This is because there are certain conditions that must obtain for adequate epistemic access to certain truths, and we must meet such conditions of reasonable epistemic access in order to reliably and justifiably make a noseeum inference. Due to the nature of dust, we do not meet the conditions of epistemic access that would allow us to make this noseeum inference.
The inference in the example above is of the form:
I do not (else: cannot) see/conceive of X, therefore (probably) there is no X.
However, arguably we must first show why we have adequate epistemic access to X in order to reliably and justifiably make this inference. We must ask: If there were an X, would we expect to see it? If there were germs on the needle, would we expect to see them? If there were dust in the room, would we expect to see it? If there were a God-justifying reason for allowing certain evil (tokens or types of) states of affairs to obtain, would we expect to see such a God-justifying reason?
Another way to put it:
If there were a P, would we know it? If there were a God-justifying reason, would we know it?
Skeptical theists, in short, argue that because there is such a staggering and vast cognitive chasm between our finite intellects and God’s infinite intellect, we shouldn’t expect to see/know his justifying reasons for everything he does/allows. We do not have reasonable epistemic access to such God-justifying reasons, and thus the atheist’s inference is a poor one. Skeptical theists will also emphasize that this cognitive chasm means that we humans do not have knowledge of the full range of possible goods and evils and the logical connections between and among them — and that because of this, we cannot justifiably arbitrate on whether or not there are God-justifying reasons.
However, this is just a single (but very illustrative) example of a more general way to undercut an argument. Whether or not skeptical theism succeeds is beside the point. The point is, rather, to illustrate a real example of undercutting defeaters in action.
If you want to undercut an argument, you can remove the justification for its premise(s), or you can remove the justification for its inference(s). In short, if you encounter a proposition, inference, or argument, inquire:
- Why should we believe this? What reasons do we have for supposing this to be true?
And, more relevant to this particular way to assess an argument:
- How do you know? Why does your justification actually support the premise in question? How does it support it?
Don’t worry — skeptical theism will be explored in much greater depth in later posts!
(2) Faulty/vague/ambiguous definitions, terms, or propositions
Example: Science and religion are incompatible.
What does this mean by science? Does it mean the process of science, its methodology? Its assumptions? The body of evidence that science has uncovered? Scientific theories? Which ones?
What does this mean by religion? Does it mean religion as a sense of spirituality and a mere belief in a transcendent being? Or does it mean a particular religion that makes certain empirical claims? Which one?
What does it mean by incompatible? Does it mean contradictory? Or that the two probably cannot co-exist? Or that religious claims have to be molded to fit the science rather than being outright concordant with them?
Example: Flying planes can be dangerous.
Is the act of piloting and flying a plane dangerous? Or are the planes themselves that are flying the ones that are dangerous?
Example: Naturalism and atheism can be defined as identical to materialism.
This is not true. Both atheism and naturalism are broader in that they allow for non-physical things to exist.
Stay tuned for more ways to assess and evaluate arguments!