J. BENTHAM, RATIONALE OF JUDICIAL EVIDENCE
from The Works of Jeremy Bentham 473-479 (Browning ed. 1842), as quoted in 8 Wigmore, Evidence §2291, pp.549-551 (McNaughton rev. 1961)
When in consulting with a law adviser, attorney or advocate, a man has confessed his delinquency, or disclosed some fact which, if stated in court, might tend to operate in proof of it, such law adviser is not to be suffered to be examined as to any such point. The law adviser is neither to be compelled, nor so much as suffered, to betray the trust thus reposed in him. Not suffered? Why not?
Oh, because to betray a trust is treachery; and an act of treachery is an immoral act.
But if such confidence, when reposed, is permitted to be violated, and if this be known, (which, if such be the law, it will be), the consequence will be, that no such confidence will be reposed. Not reposed?--Well: and if it be not, wherein will consist the mischief? The man by the supposition is guilty; if not, by the supposition there is nothing to betray: let the law adviser say every thing he has heard, every thing he can have heard from his client, the client cannot have any thing to fear from it. That it will often happen that in the case supposed no such confidence will be reposed, is natural enough: the first thing the advocate or attorney will say to his client, will be,--Remember that, whatever you say to me, I shall be obliged to tell, if asked about it. What, then, will be the consequence? That a guilty person will not in general be able to derive quite so much assistance from his law adviser, in the way of concerting a false defence, as he may do at present....
... A rule of law which, in the case of the lawyer, gives an express license to that wilful concealment of the criminal's guilt, which would have constituted any other person an accessory in the crime, plainly declares that the practice of knowingly engaging one's self as the hired advocate of an unjust cause, is, in the eye of the law, or (to speak intelligibly) in that of the law-makers, an innocent, if not a virtuous practice. But for this implied declaration, the man who in this way hires himself out to do injustice or frustrate justice with his tongue, would be viewed in exactly the same light as he who frustrates justice or does injustice with any other instrument.