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The United Kingdom Council for Graduate Education's conclusion that the traditional PhD thesis may be out of date (THES, September ) is surely fallacious. It does not follow that "differences in the composition of the candidate's thesis via the two routes [those of the traditional thesis and on the basis of published research] call into question the current relevance of a traditional thesis".

For most full-time PhD students, the writing of a thesis is a major task in which ideas, results and information collected over an extended period are brought together. In particular it ensures that where collaborative research has been undertaken, the contribution of the student can be distinguished and examined. This is not to deny that a substantial collection of published work should not be acceptable for the award of a doctorate. The two routes are not incompatible; they are just appropriate to different candidates.

K. B. Tanner Department of physics, University of Durham.