64 HARVARD LAW REVIEW. vail unless the heir-at-law established the incompetency of the testator, and, if the evidence made it a measuring cast and left them in doubt, they ought to find for the defendant. The court held, on the contrary, that while the presumption of sanity freed the defendant from the need of proof in the first instance, it did not relieve him of the fixed, unshifting burden of making out his case of a valid will. In this case there is much talk about whether the presumption of sanity be a presumption of law or of fact. Is not this an idle discussion t There is no rule of legal reasoning which is more commonly called a presumption of law than this, which, prima facie, attributes sanity to human beings. That it is a rule of presumption and a legal rule there is no doubt. The important question in any particular instance is what is the effect and operation of the rule, not what its name is. And in Sutton V. Sadler the result is that where the case is an affirmative one, the effect of this legal rule of presumption, on a part of the actor s case, is that of making out a prima facie case on this part, and not that of shifting or otherwise affecting the burden of establish- ing this part of the case. It is true then that " presumptions shift the burden of proof," in the sense of the duty or going forward with evidence. And in this sense they relieve at the outset, as touching the thing pre- sumed, him who has the duty of establishing ; they are always levamen pyobationis. It is also true that rules of presumption may fix the duty of establishing, because they are rules of law ; and a rule of law which determines who has the affirmative case may be cast in the form of a presumption ; this is a very common form of expressing all sorts of rules of law. But it is not the nature of rules of presumption, simply as such, to determine the duty of establishing the thing presumed, while it is their nature to fix the duty of meeting the presumption, 2>.,of coming forward with argu- ment or evidence. When, therefore, if ever, a rule of presumption does fix the duty of establishing, it is because of what maybe called an outside reason, e. g.^ the existence of a statute or a rule of the substantive law which imparts to the presumption this quality of determining the affirmative side ; or, to speak exactly, it is the statute or the substantive law that determines it, and not the rule of presumption.! It must be firmly held in mind that rules
- To illustrate what is meant by this, let me refer to a passage in Professor Langdell's
powerful and remarkable book on Equity Pleading (3 ed.), ss. 117 and 118. In actions
