We rediscuss the recent controversy on a possible Chern-Simons like term
generated through radiative corrections in QED with a CPT violating term. We
emphasize the fact that any absence of an {\sl a priori} divergence should be
explained by some symmetry or some non-renormalisation theorem : otherwise, no
prediction can be made on the corresponding quantity.Comment: 7 pages, LaTex file, 2 references adde