My attention was drawn to an editorial in Nature about the phrase “necessary and sufficient” in neuroscience papers (via @sophiejveigl):
If a gene is necessary and sufficient for something (as often claimed), strict logic demands that that gene alone can do the job. For example, the gene eyeless is certainly necessary for a retina to develop. But it is not sufficient — if it were, then logic would demand that ‘if eyeless exists, then a retina will develop’. This is false; other genes and factors are needed as well. Yet eyeless is often described as being necessary and sufficient for retinal development.
The suggestion discussed in the editorial is that genes should instead be called “indispensable and inducing”. This is sensible as far as it goes, since the connotation of “inducing” is that the gene causes the expression of the trait, but that it does not do so invariably — only in appropriate background circumstances, that is, in conjunction with a set of further genes and other relevant conditions. “Indispensable” captures the methodological strategy that the relationship between a gene and a trait is demonstrated by suppressing the gene in a controlled experiment, to see whether the trait disappears as well.
But why not just say that “the gene causes the expression of the trait”? I am not aware of any influential analysis of causation that suggests that causes are individually sufficient. For my part, I think that the INUS analysis is quite handy for everyday occasions (I teach it to students of biology and medicine). On the INUS analysis, a cause is an Insufficient but Necessary part of a condition that is Unnecessary but Sufficient for an effect.
This is a mouthful, but easy to understand by example. Aspirin, in suitable background circumstances, relieves headaches. (It is individually insufficient for the effect, but a necessary part of a jointly sufficient condition.) But other interventions (a warm bath) can also relieve headaches within their own sufficient set of circumstances. (So each sufficient set of circumstances is individually unnecessary.)
So you see, editors of Nature, you already have le mot juste. It is the humble “causes”. Why would this not serve biologists well?
Raphael Scholl 