  The second option is eliminated with the observation that although I clearly can cause some ideas at will (e.g. ideas of imagination), sensory ideas are involuntary; they present themselves whether I wish to perceive them or not and I cannot control their content. The hidden assumption here is that any causing the mind does must be done by willing and such willing must be accessible to consciousness. Berkeley is hardly alone in presupposing this model of the mental; Descartes, for example, makes a similar set of assumptions. 