This post is intended to briefly describe Drestke’s characterization of the paradox of mediate knowledge in his paper, “Perception and Other Minds”, and to apply the concept to three different cases. (1) Knowledge of the external world, (2) knowledge of the unobserved, (3) knowledge of other minds. This is not intended to be a defense of anyone’s argument, but I will link to other posts containing relevant arguments.
…either P is the sort of thing that can be known immediately (non-inferentially, directly, with no evidential basis) or it is the sort of thing that can’t be known at all. For suppose P is the sort of thing that is known indirectly – on the basis, say, of Q-states. If P is to be known on the basis of a Q-state, then a Q-state must be a more or less reliable sign, indicator, or symptom of a P-state, and this fact must itself be known or, at least, reasonably well-established. But the fact that a Q-state is a reliable sign of a P-state can never be known. We can never know this because we can never determine whether a P-state exists when a Q-state exists since a P-state is not (by hypothesis) directly knowable, and to know that it exists indirectly is to know that it exists on the basis of a Q-state which assumes the validity of the very correlation that is in question. Since we cannot tell whether P exists except via Q, we have no way of telling that the correlation between P and Q is as we must assume it to be in knowing that P is the case on the basis of Q. Therefore, P cannot be known even on the basis of Q.
So it doesn’t seem like indirect knowledge is possible. Because there is always some sign or somesuch x that stands between us and direct knowledge of what is so, but is somehow supposed to be an indicator of what is so. But we can never reliably establish the fact that the sign truly indicates the corresponding object. And all we can ever have knowledge of is the sign, so we can never really know about the object for which it stands. This sort of situation happens in many areas of perceptual knowledge, and I will discuss three.
- Knowledge of the external world.
Descartes fashioned his evil genius illusion scenario, and Russell posited his sense-data. Both of these are the Q-states, which are purportedly signs of things in the mind-independent world around us. We infer from sense-data to presence of an actual object. But this inference is not wholly justified, for we have no reason to suppose that the mind-independent object faithfully corresponds to the appearance in our sense-data. And so the skeptical paradox arises: how can we have any knowledge of the external world?
2. Knowledge of the unobserved.
Hume is the most famous skeptic of our knowledge of the unobserved. All we ever get in experience is constant conjunction of some A followed by some B. Some examples: My hand feels hot when it is over the fire | there is constant conjunction between my hand over the fire and my sensation of heat. One billiard ball moves toward another and causes the other to move | there is a constant conjunction between the striking of two balls and the movement thereafter. The sun rises every morning | there is a constant conjunction between the sun rising and certain interval of time.
Here, constant conjunction will be the Q-state. On the basis of our experience and direct knowledge of constant conjunction, we make an inference to there being some genuine causal relation. But we cannot establish a definitive link between constant conjunction and causal connection, and so our inference cannot be justified. And when our belief in causal connection is unjustified, then we get the skeptical paradox: how can we have any knowledge of unobserved events?
3. Knowledge of other minds.
How do we know that another person has a mind? Presumably we watch them perform intentional actions, like going for a walk or weaving a basket underwater. We hear them say “ouch!” when they’re in pain. And so on. These are the things for which we have direct knowledge. But on one level, these seem no more than mere behavioral signs (the Q-states). On the basis of these observations of behavioral signs, we infer that some agent has genuine mental states. To know that “ouch” is a sign of genuine pain, we need to know that there is a connection between an other’s saying “ouch” and their being in a genuine state of pain. But it is this connection that we cannot know (and indeed are trying to establish). The inference from behavioral signs to mental states will be unjustified. So how can we ever have any knowledge of other minds?
A way forward.
So we see how the paradox of mediate knowledge generates skepticism in three domains of perceptual knowledge. One solution might be to simply eliminate Q-states all together. We do not directly perceive sense-data and indirect perceive mind-independent objects; we simply directly perceive the mind-independent objects. We do not see only constant conjunction and so have indirect knowledge of cause; we simply directly perceive the relevant causal relations. We do not see behavioral signs from which we infer the presence of a mind; we simply directly perceive the minded-ness of the other individual. I do not mean to argue for this thesis presently, but just offer it as something to think about in response to the paradox of mediate knowledge.