"If you want to get into the technicalities, yes - but some oaths are easier to break than others - particularly if you go into one with appropriate clauses! But... we swore, my brothers and my father and I, by the highest authority of our world, and called upon ourselves the most terrible fate. For love, for grief, I swore it, and none made me do so, although I knew that it would only bring grief. Too late I realised exactly how terrible the darkness I had called upon myself was, and by then it was too late. I committed terrible atrocities in the name of that Oath, Doctor. And until I came to Asgard, I felt it like hooks in my soul, driving me on no matter how terrible the deeds and how little I wished to do them. It killed my family, that Oath, and at the last my eldest brother could no longer bear it, and killed himself to find some peace."