Thus the _Vyāsa-bhāshya_, IV. 14, says: “There is no object without the knowledge of it, but there is knowledge as imagined in dreams without any corresponding object; thus the reality of external things is like that of dream-objects, mere imagination of the subject and unreal. How can they who say so be believed? Since they first suppose that the things which present themselves to us by their own force do so only on account of the invalid and delusive imagination of the intellect, and then deny the reality of the external world on the strength of such an imaginary supposition of their own.” The external world has generated knowledge of itself by its own presentative power (_arthena svakīyayāgrāhyaśaktyā vijñānamajani_), and has thus caused itself to be represented in our ideas, and we have no right to deny it.[20] Commenting on the _Bhāshya_ IV. 14, Vācaspati says that the method of agreement applied by the Buddhists by their _sahopalambhaniyama_ (maxim of simultaneous revelation) may possibly be confuted by an application of the method of difference. The method of agreement applied by the idealists when put in proper form reads thus: “Wherever there is knowledge there is external reality, or rather every case of knowledge agrees with or is the same as every case of the presence of external reality, so knowledge is the cause of the presence of the external reality, i.e. the external world depends for its reality on our knowledge or ideas and owes its origin or appearance as such to them.” But Vācaspati says that this application of the method of agreement is not certain, for it cannot be corroborated by the method of difference. For the statement that every case of absence of knowledge is also a case of absence of external reality cannot be proved, i.e. we cannot prove that the external reality does not exist when we have no knowledge of it (_sahopalambhaniyamaśca vedyatvañca hetū sandigdhavyatirekatayānaikāntikau_) IV. 14.