Both Melanie Klein and Lacan were to adopt versions of the death drive in their own theoretical constructs. "Klein's concept of the death drive differs from Freud's ... but there is an ever-increasing reference to the death drive as a given cause of mental development"[45] in her works. Lacan for his part considered that "the death drive is only the mask of the symbolic order, in so ... far as it has not been realised", adding modestly of Beyond the Pleasure Principle "... either it makes not the least bit of sense or it has exactly the sense I say it has".[46]