 There have been substantial debates over the symmetricality question (Brock 1991; Buller 2001; Cale 1999; Checkland 2001; Skene 1991; Wicclair 1991, 1999; Wilks 1997, 1999). A key feature of the debate is whether or not mental capacity should be considered a fixed mental commodity (Buchanan &amp; Brock 1989: 60). In other words, relative to a particular yes-or-no decision such as the one described above, should we articulate a single threshold (a certain level or degree of understanding, appreciation, etc. that the patient must have) such that any patient above the threshold should be free to either consent or refuse? Or is it better to view such a choice as two different decisions and so articulate two different thresholds, one for acceptance and one for refusal, setting the threshold higher for those patients inclined to refuse?