Coherence theories of justification all face several well-known objections. While I believe that these objections all center around a common theme, that’s for another post. In this one, I’m going to discuss the input problem and how a coherence theory can overcome it.
The input problem states that a coherence theory entails that justification supervenes onto the internal state of a doxastic system, where the internal state is coherence. This raises the question of what the world external to the system has to do with justification. It seems natural to think that justification of beliefs about the world external to those beliefs requires some input from the world. This is the essence of the input problem.
There are several arguments from prominent coherentists that seem to entail that the world external to the doxastic system cannot play an epistemic role in justifying the beliefs in the system. Instead, the external world is merely a causal factor. Humans see a table in front of them and that visual appearance causes them to form the belief “I see a table in front of me”. One famous argument is from Donald Davidson,
“The relation between a sensation and a belief cannot be logical, since sensations are not beliefs or other propositional attitudes. What then is the relation? The answer is, I think, obvious: the relation is causal. Sensations cause some beliefs and in this sense are the basis or ground of those beliefs. But a causal explanation of a belief does not show how or why the belief is justified” (Davidson 1986).
The argument is that appearances or sensations are not the sorts of things that can logically entail things, and the only things capable of conferring justification are things that have some propositional structure, or just some truth-evaluable content. So, the only role sensations can play is that of a cause of beliefs or other propositional attitudes.
A way for a coherentist to resist this line of reasoning is to recognize that appearances and other experience states have truth-evaluable content. While appearance states are not beliefs, they do have content that is capable of accuracy or error. Since they have content that’s truth-evaluable, there is nothing wrong with defining coherence as a relation between both beliefs and appearance states. This response leads to the best way for a coherentist to overcome the input objection.
Appearances are states that have contents about the world external to the subject. Since appearance states allow for content about the world into the system, they allow for a response to the input objection. The way that appearance states can play a role in the coherence theory is by way of INUS conditions (Kvanvig and Riggs 1992). J.L. Mackie introduced this notion in his famous analysis of causation. An INUS condition is an insufficient but necessary and non-redundant part of an overall unnecessary but sufficient condition. So, an INUS condition for some explosion was the presence of oxygen in the air at the time.
In the context of appearance states, they are an INUS condition for observational beliefs being justified. While some may hold that they are INUS conditions for all beliefs having such status, that’s unnecessary for the purpose of overcoming the input objection. For some observational belief P to have positive epistemic status, it’s necessary but insufficient that the subject be in some appearance state whose content is captured by the contents of the belief.
Seeing appearance states as INUS conditions solves the problem of input. This is not to imply that appearance states are things that are capable of being justified. Rather, they are necessary and non-redundant parts of an overall unnecessary but sufficient condition for some beliefs being justified. The objects of epistemic appraisal are not appearance states. However, they are necessary for observational beliefs being justified. So, the input problem is overcome, and coherentists can define coherence over appearance and other experiential states as well as beliefs.
Davidson, Donald. (1986). “A Coherence Theory of Truth and Knowledge”. Truth and Interpretation: 307-319. Print.
Kvanvig, Jonathan L., and Wayne D. Riggs. (1992). “Can a Coherence Theory Appeal to Appearance States?” Philosophical Studies: 197-217. Print.