  This change of stance was accompanied by a further significant evolution in doctrine. Brentano subscribed to a two-component conception of consciousness: in perceiving an object, we are aware not only of the object presented in perception, but also of our perceiving of that object. Hence in any perceptual act, e.g. the hearing of a tone C, there are two ingredients: the primary object of the act, the tone C, and the secondary object, which in this case is the hearing of C. In virtue of this two-fold structure, consciousness at a given moment of time is always accompanied by a form of self-consciousness. But what of the diachronic case? Does this mode of self-consciousness extend over time? Brentano’s views on this also underwent changes. On his early ‘object modification’ view, he held that the primary object of a proteraesthesis is an earlier act of experiencing: e.g., a past sensing of tone C, rather than C itself. In virtue of this, we have a continuous awareness of our own conscious acts over time as well as at a time, although the mechanism in the diachronic case (involving primary objects) differs from that which operates in the synchronic case (which relies on secondary objects). However, Brentano came to regard this as a mistake, and in his mature ‘temporal mode of presentation’ account, the primary object of the proteraesthesis is no longer the act of sensing C, but C itself, albeit presented under the mode of ‘having occurred in the past’.