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### Ideas of Paul Thagard, by Text

 1989 Explanatory Coherence
 1 p.4 17064 1: Coherence is a symmetrical relation between two propositions Full Idea: 1: Coherence and incoherence are symmetrical between pairs of propositions. From: report of Paul Thagard (Explanatory Coherence [1989], 1) by J.J.C. Smart - Explanation - Opening Address p.04
 2 p.4 17065 2: An explanation must wholly cohere internally, and with the new fact Full Idea: 2: If a set of propositions explains a further proposition, then each proposition in the set coheres with that proposition, and propositions in the set cohere pairwise with one another. From: report of Paul Thagard (Explanatory Coherence [1989], 2) by J.J.C. Smart - Explanation - Opening Address p.04
 3 p.4 17066 3: If an analogous pair explain another analogous pair, then they all cohere Full Idea: 3: If two analogous propositions separately explain different ones of a further pair of analogous propositions, then the first pair cohere with one another, and so do the second (explananda) pair. From: report of Paul Thagard (Explanatory Coherence [1989], 3) by J.J.C. Smart - Explanation - Opening Address p.04
 4 p.4 17067 4: For coherence, observation reports have a degree of intrinsic acceptability Full Idea: 4: Observation reports (for coherence) have a degree of acceptability on their own. From: report of Paul Thagard (Explanatory Coherence [1989], 4) by J.J.C. Smart - Explanation - Opening Address p.04 A reaction: Thagard makes this an axiom, but Smart rejects that and says there is no reason why observation reports should not also be accepted because of their coherence (with our views about our senses etc.). I agree with Smart.
 5 p.4 17068 5: Contradictory propositions incohere Full Idea: 5: Contradictory propositions incohere. From: report of Paul Thagard (Explanatory Coherence [1989], 5) by J.J.C. Smart - Explanation - Opening Address p.04 A reaction: This has to be a minimal axiom for coherence, but coherence is always taken to be more than mere logical consistency. Mutual relevance is the first step. At least there must be no category mistakes.
 6 p.4 17069 6: A proposition's acceptability depends on its coherence with a system Full Idea: 6: Acceptability of a proposition in a system depends on its coherence with the propositions in that system. From: report of Paul Thagard (Explanatory Coherence [1989], 6) by J.J.C. Smart - Explanation - Opening Address p.04 A reaction: Thagard tried to build an AI system for coherent explanations, but I would say he has no chance with these six axioms, because they never grasp the nettle of what 'coherence' means. You first need rules for how things relate. What things are comparable?
 2012 Coherence: The Price is Right
 p.42 p.42 17596 Coherence problems have positive and negative restraints; solutions maximise constraint satisfaction Full Idea: A coherence problem is a set of elements connected by positive and negative restraints, and a solution consists of partitioning the elements into two sets (accepted and rejected) in a way that maximises satisfaction of the constraints. From: Paul Thagard (Coherence: The Price is Right [2012], p.42) A reaction: I'm enthusiastic about this, as it begins to clarify the central activity of epistemology, which is the quest for best explanations.
 p.43 p.43 17597 Coherence is explanatory, deductive, conceptual, analogical, perceptual, and deliberative Full Idea: I propose that there are six main kinds of coherence: explanatory, deductive, conceptual, analogical, perceptual, and deliberative. ...Epistemic coherence is a combination of the first five kinds, and ethics adds the sixth. From: Paul Thagard (Coherence: The Price is Right [2012], p.43) A reaction: Wonderful. Someone is getting to grips with the concept of coherence, instead of just whingeing about how vague it is.
 p.44 p.44 17598 Explanatory coherence needs symmetry,explanation,analogy,data priority, contradiction,competition,acceptance Full Idea: Informally, a theory of explanatory coherence has the principles of symmetry, explanation, analogy, data priority, contradiction, competition and acceptance. From: Paul Thagard (Coherence: The Price is Right [2012], p.44) A reaction: [Thagard give a concise summary of his theory here] Again Thagard makes a wonderful contribution in an area where most thinkers are pessimistic about making any progress. His principles are very plausible.
 p.45 p.45 17599 The best theory has the highest subjective (Bayesian) probability? Full Idea: On the Bayesian view, the best theory is the one with the highest subjective probability, given the evidence as calculated by Bayes's theorem. From: Paul Thagard (Coherence: The Price is Right [2012], p.45)
 p.45 p.45 17600 Bayesian inference is forced to rely on approximations Full Idea: It is well known that the general problem with Bayesian inference is that it is computationally intractable, so the algorithms used for computing posterior probabilities have to be approximations. From: Paul Thagard (Coherence: The Price is Right [2012], p.45) A reaction: Thagard makes this sound devastating, but then concedes that all theories have to rely on approximations, so I haven't quite grasped this idea. He gives references.
 p.46 p.46 17602 Verisimilitude comes from including more phenomena, and revealing what underlies Full Idea: A scientific theory is progressively approximating the truth if it increases its explanatory coherence by broadening to more phenomena and deepening by investigating layers of mechanisms. From: Paul Thagard (Coherence: The Price is Right [2012], p.46)
 p.46 p.46 17601 Neither a priori rationalism nor sense data empiricism account for scientific knowledge Full Idea: Both rationalists (who start with a priori truths and make deductions) and empiricists (starting with indubitable sense data and what follows) would guarantee truth, but neither even begins to account for scientific knowledge. From: Paul Thagard (Coherence: The Price is Right [2012], p.46) A reaction: Thagard's answer, and mine, is inference to the best explanation, but goes beyond both the a priori truths and the perceptions.