As with most formal results applied to philosophical issues, the crucial questions concern the assumptions on which the proof rests. Alternately, we might say that while coherence exists, it cannot satisfy the epistemological hopes that made us interested in it. Taking truth-conduciveness as essential to the concept of coherence, he concludes that coherence does not exist. It is here that he reveals his most dramatic result: Olsson shows that, subject to several seemingly reasonable assumptions, it is impossible to define any such measure. In the second part of the book, Olsson addresses himself to the effort to define a measure of coherence on which more coherent belief systems are, ceteris paribus, more likely to be true. If we place the burden of proof on the skeptic, this kind of reply may be all we need. While Olsson is correct that none of the authors he critiques have shown the relevant forms of skepticism to be false, those authors may nevertheless have accomplished something of value: they have explained how our beliefs could be justified, in the face of skeptical arguments to the contrary.

As Olsson notes, this assumption is particularly problematic in the case of memory beliefs, which do in fact influence each other (if one 'remembers' that P, whether correctly or not, one is more likely to 'remember' other things consistent with P). Second, neither Lewis, nor Coady, nor BonJour provides arguments to justify the needed assumption that the 'reports' generated by our cognitive faculties are probabilistically independent of each other.

Without this, they lack a convincing reply to the skeptic, since they cannot show that beliefs based on memory or testimony are sufficiently probable to pass the threshold for justified belief. First, how likely it is that a coherent set of beliefs is accurate depends on the degree of individual credibility of those beliefs, and neither Lewis nor Coady provide any way of determining the relevant degrees of credibility. Once we grant individual credibility to some external world beliefs, we have abandoned a central motivation for coherentism and fallen into what BonJour called 'weak foundationalism'.Įven if we accept some degree of individual credibility, as both Lewis and Coady do, two problems remain. This fact creates a problem for BonJour, who sought to justify external-world beliefs solely on the basis of coherence, without the need for individual credibility. As Olsson shows, however, this intuitive result holds only as long as each witness has at least some degree of individual credibility (meaning that receiving the testimony of one witness raises the probability of what the witness asserts). Similarly, the coherence of a set of independently acquired beliefs is thought to provide justification for thinking that those beliefs are by and large true. Intuitively, the witnesses' agreement constitutes strong evidence that the story to which they attest is the truth. He takes as a starting point an illustration employed by both Lewis and BonJour, in which witnesses of doubtful reliability independently agree on a number of specific details about a crime. Coady to use coherence to justify our ordinary beliefs derived, respectively, from memory, sense perception, and testimony.

In the first part of the book, Olsson confronts attempts by C.I. Ultimately, he finds that a high degree of coherence cannot secure a high probability of truth, nor does greater coherence in general imply a greater likelihood of truth, even ceteris paribus. Olsson focuses on attempts to show that coherence is 'truth-conducive', meaning that the coherence of a belief system contributes to its probability of being accurate. Erik Olsson's Against Coherence poses a powerful challenge to coherence theories of justification, from the standpoint of probabilistic epistemology.

Coherence theory of truth in philosophy