The second type of causal law takes the following form: “X is the sole cause
of Y.’ This sets up a syllogism in the following form:
Components
Relationships
Major Premise
X is the sole cause of Y
Minor Premise
Y has occurred
Conclusion
Therefore X occurred beforehand.
Figure 23.3 Syllogism: X Always Causes Y
Let us summarise this. If the rule is “X always causes Y” then when X occurs,
Y will occur after. If the rule is “X is the sole cause of Y” then when Y occurs,
X will have occurred beforehand.
Estimating Probability
In principle the method of deduction yields incontrovertible truth. This occurs
when each of the premises is true in fact and the reasoning process is sound.
In the form of deduction above, the reasoning process is sound, but the truth
of the premises is not always beyond question.
The minor premise of the syllogism involves a claim that a fact, Fact X or Fact
Y, is true. Let us call this the foundational fact. The truth of Fact X or Fact Y
can be established by any of the means for proof. In many cases it will be
established by observation, for example, it is observed at the scene of a crime.
However, there is no guarantee that this fact is established to a 100%
uncertainty even though in many cases its existence is beyond doubt.
The major premise of the rule involves a scientific rule is true. This rule can be
in the firm “X always causes Y” or “X is the sole cause of Y”. In some cases
this rule will be, for practical purposes at least, established to a certainty that at
least is very near 100%.
This said, often there is some testing procedure that is needed to apply the
rule. Even
if the science underlying the procedure is 100% certain (or near
enough) the testing procedure may not be anywhere near as certain as this.
This happens because sometimes the technology is not sufficiently developed.
Thus while this method of estimating the probability that facts are true
possesses a deductive form it may not always yield deductive certainty.
Having laid out the process for truth it is possible now to see how to estimate
the probability that the fact derived by the process (the derived fact, DF) is
true. It depends on three probabilities:
(1)
The probability that the foundational fact is true: P(FF).
(2)
The probability that the relevant scientific rule is true: P(SR).
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