Thus far, I have surveyed “the good” and “the bad” sides of David Hume’s famous argument against miracles (see here and here). That leaves “the ugly”: Hume’s circular definition of what a miracle is.

To the point, for Hume “[a] miracle is a violation of the laws of nature” (Hume, Of Miracles, para. 12; cf. Voltaire 1764/1901, p. 272). Alas, the problem with Hume’s definition is that it is circular! Why is this definition a circular one? Because unlike human laws, which are defied and disregarded all the time, “laws of nature” consist of patterns or regularities that can never be set aside or suspended. In other words, a violation of a law of nature has, by Hume’s own definition, a probability of zero!

To see why, ask yourself two deeper questions: (1) what is a “law of nature” (see here, for example), and (2) what does it mean to “violate” or disobey such a thing? Although Hume himself uses the term “laws of nature” in several different senses (see here), at a minimum a law of nature in the traditional Newtonian sense (see, e.g., “Newton’s Three Laws of Motion“) generally refers to some uniform or regular pattern of behavior. On this view of “natural law”, a miracle must consist of an unforeseen departure from or an unexpected interruption of such a pattern.

By way of illustration, consider Newton’s First Law: “Corpus omne perseverare in statu suo quiescendi vel movendi uniformiter in directum, nisi quatenus a viribus impressis cogitur statum illum mutare.”(Translation: “Every object perseveres in its state of rest, or of uniform motion in a right line, unless it is compelled to change that state by forces impressed thereon.”) In plain English, this law tells us that objects tend to “keep on doing what they’re doing” until they are acted upon by an outside force. The dirty clothes in your hamper, for example, will remain there until someone grabs them and throws them in the washing machine.

Maybe you agree with Hume’s circular definition of miracles. After all, what if your clothes did wash themselves? That would be a true miracle! But from a purely logical perspective, the problem with Hume’s definition is that he’s rigged the game ex ante. To see why, recall Hume’s two-part probability test for miracles: 1st, given some evidence that a miracle took place, Hume would have us assign two separate probability values to the evidence — the probability p₁ that the miracle really happened and the probability p₂ that the evidence is either mistaken or fraudulent or otherwise defective — and 2nd, Hume would have us compare p₁ and p₂: you should believe in the miracle only if p₁ > p₂.

The problem, however, is this: under Hume’s natural-law-violation definition of miracles, p₁ = 0, no amount of evidence of whatever kind would ever be sufficient to establish the occurrence of a miracle, a truly dogmatic and closed-minded position to take, especially when we have so many reports of miracles from so many different sources! Nevertheless, that said, it takes a theory to beat a theory, so in my next post, I will present an alternative method for evaluating incredible claims of miracles.