A critical method for interpreting strong evidence

19 October 2002 (Incomplete)

    This essay is part of a new group of expositions of the critical method and how it can be used in the JFK assassination. The series begins with the general critical method and its classical roots. It continues with an adaptation of the method to validating physical evidence and thereby producing "strong: evidence. This essay shows how to use the critical method to interpret validated physical evidence (or "strong" evidence). In so doing, it complements the previous one on validation and completes the two-part series of dealing with physical evidence.
    Here is the version of the critical method suited to interpreting strong evidence.

1. Ask a question about a pieces of strong evidence. (Example: "Does the Zapruder film prove that JFK was hit in the head from the rear?")
2. List all possible preconceived answers (hypotheses) on the meaning, no matter how bizarre or biased. [This step incorporates the "multiple working hypotheses" approach, which is designed to maximize the range of possible explanations considered and minimize early bias toward any particular explanation. See "Multiple working hypotheses—formal statement" and "Multiple working hypotheses—informal statement."]
3. Assemble all relevant evidence. 
4. Divide the evidence into "strong" and " weak," where "strong" means objectively validated (physical evidence that has passed the process described in "A critical method for validating physical evidence"), and "weak" means of a type that cannot be objectively validated (all witness evidence, any physical evidence that has not yet been validated, and many expert judgments). (See "Types of Evidence Useful for Understanding the JFK Assassination") 

    Strong evidence only

5. List all possible answers, however unlikely, consistent with the strong evidence.
6. Choose the simplest answer consistent with all the strong evidence. (This step is the application of the famous "Occam’s razor," otherwise known as the Principle of Parsimony. It does not necessarily mean, as many think, that the simplest answer is most likely to be right. Rather, it represents the obligatory starting point, for no meaningful explanation may contain any provision that does not explain something, or "work."). This provisional answer is called the "working hypothesis."
7. Test this working hypothesis rigorously against its consequences (predictions) or against new evidence that arises (often gathered explicitly for the purpose).
8. Consider the working hypothesis proved if it passes all the tests and no other answer is possible. (Uncommon.) Then go to step 12.
9. Retain the working hypothesis if it passes all the tests but other answers are possible. Then go to step 12.
10. Reject the working hypothesis if it fails one or more of the tests. Then choose the next-simplest answer and return to step 7 to test it.
11. Continue cycling through steps 7-10 until you find the simplest hypothesis that survives all the tests. Be your own strongest critic. (If two or more successful hypotheses are equally simple, retain them as advanced multiple working hypotheses.) Then go to step 12.

    Strong and weak evidence (Steps 12 through 19 are for cases where you wish to or need to add weak evidence to the mix, usually when the external strong evidence is minimal and insufficient to interpret the evidence in question and expert opinion must be turned to. If there is enough strong evidence to unambiguously interpret the evidence in question, proceed to step 20.)

12. Add selected weak evidence, often as expert testimony, to the strong evidence. Remember that this will downgrade any resulting answer to "speculative and without logical force."
13. List all possible answers consistent with the strong and weak evidence.
14. Choose the simplest answer consistent with all the evidence.
15. Test this working hypothesis against its consequences (predictions) or against new evidence that arises.
16. Consider the working hypothesis proved if it passes all the tests and no other answer is possible. Go to step 20.
17. Retain the working hypothesis if it passes all the tests but other answers are possible. Go to step 20.
18. Reject the working hypothesis if it fails one or more of the tests. Choose the next-simplest answer and return to step 15 to test it.
19. Continue cycling through steps 15-18 until you find the simplest hypothesis that survives all the tests. (If two or more successful hypotheses are equally simple, retain them as multiple working hypotheses.) Go to step 20.

    Either set of evidence

20. Continue testing the successful hypothesis (or hypotheses) against new evidence as it appears. Status of answer: reliable if from strong evidence only, speculative and unreliable if from strong and weak evidence.

Examples

    What does the Zapruder film show about the direction that JFK's head was hit from?
    Possible answers: From front; from rear; from both directions.
    Relevant strong evidence:
        JFK's head snaps forward just before it explodes (something hit it from the rear).
        Mrs. Kennedy showed no such motion (so JFK's motion wasn't from an acceleration of the car).
        Physics calculations show that the speed of the snap is consistent with the WCC/MC bullet fired from Oswald's rifle and later retrieved from the front seat (the only bullet traced to the head, via NAA, could have accounted for the motion).
        The two largest fragments of skull flew out in the forward direction (some kind of major impulse came from the rear).
        The fine spray of fluids and particles flew forward (major impulse from the rear).
        A large flap of scalp and possibly skull, presumably related to the wound of exit, hung down over and in front of his right ear (exit wound in the front half of the head).
        There was no such breakage at the rear of his skull (the bullet did not exit from the rear of the skull).
        Shortly after the forward snap, JFK's head and the rest of his upper body move toward the rear (but this motion delayed long enough so that it couldn't have come directly from a bullet).
        The rearward motion of head and torso contained too much energy to come from the impact of a bullet. (So it was caused by something else.)
    Answers consistent with the strong evidence: Single hit from the rear.
    Simplest of these answers: Single hit from the rear.
    Degree of support: Very strong indirect evidence, but not proof.
    Comments: It is widely accepted that the Zapruder film proves that the head was hit from the rear. It does not. It provides extremely strong indirect evidence for it, however. Proof would require actually observing the bullet enter the head.
    Selected weak evidence: None needed.
    Final status of the answer: The extremely strong working hypothesis is retained.