What use is Morgan's canon?

Morgan's canon can be construed as claiming that an intentional explanation of a behavior should be ruled out if there exists an explanation of this behavior in terms of 'lower' mechanisms. Unfortunately, Morgan's conception of higher and lower faculties is based on dubious evolutionary considerations. I examine alternative interpretations of the terms 'higher' and 'lower', and show that none can turn the canon into a principle that is both correct and useful in drawing the line between thinkers and non-thinkers. In the process, I identify a number of problems that an adequate formulation of the canon should avoid. I then consider two more recent versions of the canon, proposed by Elliott Sober and Jonathan Bennett. Both are found unsatisfactory, but I argue that a version of Bennett's unity condition that is restricted to the attribution of recognitional concepts is on the right track