Responsa for Chullin 230:46

וליפרוך לכולהו

will you say it in that? ' can only be refuted by adducing a feature in the one which is less or more grave than in the other, and not by any peculiarity whatsoever.<span class="x" onmousemove="('comment',' Where an inference is made from the common features of two cases all the cases must indeed be alike in every respect, and if one case presents any special characteristic, even though that characteristic does not go down to the root of the matter and is of no significance, the argument is untenable. On the other hand, where the law in one case is inferred from another case, e.g. by an a fortiori argument, an incidental characteristic would not be taken into consideration. Only a characteristic which is of such significance as to suggest the reason for the law in that particular case, would be accepted as a refutation, for then it would be argued thus, 'No, if you say it in the one case, it is because it has this grave or less grave characteristic; will you say it in the other cases which have not this characteristic'?');">³⁰</span>

Teshuvot Maharam