The Fundamental Principle of the General-Specific Causation Dichotomy
The idea that there are two types of causation, one general and the other specific, is rarely enlightening but increasingly the source of confusion, mischief-making and legal bickering. Take for instance the recent per curiam and dissenting opinions in Huss v. Gayden.
In Huss the plaintiff claimed that the drug Terbutaline caused her to develop debilitating cardiomyopathy. At trial the court permitted some testimony by the defendant's expert to the effect that Terbutaline does not cause cardiomyopathy in humans but prevented him from testifying that Terbutaline did not cause Huss' cardiomyopathy. The holding on appeal was that the defendant's expert had not been allowed to fully express his views on general causation and so the case was reversed and remanded. The dissent vigorously objected, writing that the expert had indeed expressed to the jury all that needed to be said on the subject of general causation, that he was not, through education, training or experience, able to opine on the subject of specific causation and that the verdict should thereby stand.
The dissent, citing Tanner v. Westbrook, wrote that the court was required "to acknowledge the fundamental principle of the general-specific dichotomy: that a witness may be competent to testify about general causation but not specific causation." Now, before I discuss this "fundamental principle" (tomorrow) let's first think a bit about reasoning from the general to the specific.
Assume that Wilbur is a pig and the allegation is that Wilbur has been flying. My expert on pigs takes the stand and testifies "No pig can fly". This is of course a general statement about pigs; but Wilbur is a subset of pigs. My expert ought therefore be allowed to testify that Wilbur cannot fly, whether he's ever examined him or not, because what is true of pigs must necessarily be true of Wilbur. Imagine my dilemma if the dissent had its way and I was required to put on specific expert testimony to the effect that Wilbur hadn't been flying. Where exactly would I find someone with the education, training and expertise in recognizing (to paraphrase the test set out by the dissent) the prior flying habits of pigs "in a particular and unique case"?
Tanner on the other hand presents a distinctly different sort of issue. Let's go back to Wilbur. Now he's alleged to have incubated the H1N1 swine flu and given it to his owner, Zuckerman. The plaintiff's expert takes the stand and opines generally that pigs, being swine, are capable of incubating swine flu. He then concludes that Wilbur, being a pig, must have harbored the flu since he was capable of doing so and since Zuckerman now has the flu. Here the criterion of specificity is in order since not all pigs had the flu and since there were other possible non-swine vectors for Zuckerman's flu. Because plaintiff's expert never isolated antibodies to that flu strain from Wilbur's blood nor did he evince any expertise in the forensic diagnosis of H1N1 in pigs his specific causation testimony is unfounded and rightly excluded.
The real problem is that "the fundamental principle of the general-specific dichotomy" isn't fundamental because there's no real dichotomy. More on that tomorrow.
