Richard Whately, answered from the texts and cited to the page.
A presumption, properly understood, is a pre-occupation of the ground: it does not assert that one side is more likely right, only that it stands until sufficient reason is brought against it, and that the onus probandi lies on whoever would disturb it.1 Now, the burden is not fixed permanently on one side. A presumption may be rebutted by an opposite presumption, and when that occurs, the burden shifts.2
The case I give in the Elements of Rhetoric — a work concerned throughout with the logic of argumentative composition — is this: suppose you are called on to justify removing some existing restriction. There is a presumption against every change, so the burden falls initially on you, the innovator.3 But you may fairly reply that every restriction is in itself an evil, and that there is therefore a counter-presumption in favour of its removal unless its defenders can show it necessary to prevent some greater evil; and at that point it is they, not you, who must prove.4
The burden has shifted — not by rhetoric, but by the collision of two genuine presumptions. The archetype, then, is this: one party occupies the ground and the other must dislodge it; but the occupying party may itself be dislodged from that position by a counter-presumption, whereupon the roles reverse. The practical consequence is that a disputant who fails to notice this reversal may abandon a fortress he already held, march into the open field, and suffer a repulse he need never have risked.5
He who has the presumption on his side, and can refute the arguments brought against him, has already won — but only if he keeps possession of his position and does not allow the presumption to be forgotten.6 The lesson for any disputant is prior to everything else: before you argue a single point, determine on which side the presumption lies.
A body of evidence perfectly adequate to defend a position may prove quite insufficient to establish it from scratch, and a great deal of what looks like weak advocacy is simply a man who has accepted a burden that was never his to bear.
a 'presumption' in favor of any supposition means, not (as has been sometimes erroneously imagined) a preponderance of probability in its favor, but such a preoccupation of the ground as implies that it must stand good till some sufficient reason is adduced against it; in short, that the burden of proof lies on the side of him who would dispute it.Elements of Rhetoric
a presumption may be rebutted by an opposite presumption, so as to shift the burden of proof to the other side.Elements of Rhetoric
there is a presumption in favor of every existing institution... the 'burden of proof' lies with him who proposes an alteration; simply on the ground that since a change is not a good in itself, he who demands a change should show cause for it.Elements of Rhetoric
every restriction is in itself an evil; and therefore there is a presumption in favor of its removal, unless it can be shown necessary for prevention of some greater evil: I am not bound to allege any specific inconvenience; if the restriction is unnecessary, that is reason enough for its abolition: its defenders therefore are fairly called on to prove its necessity.Elements of Rhetoric
if you abandon this position, by suffering this presumption to be forgotten, which is in fact leaving out one of perhaps your strongest arguments, you may appear to be making a feeble attack, instead of a triumphant defence.Elements of Rhetoric
if you have the 'presumption' on your side, and can but refute all the arguments brought against you, you have, for the present at least, gained a victory.Elements of Rhetoric