Constrained by sensations
The state of being self-conscious of duration is ascertained by referring to something external and linked with individual existence. Such experiences issue from a stable scheme coordinating all external sensations in the mind. Any sensation requires something permanent and distinct by relation to which their variation can be interpreted.
“Through inner experience I am conscious of my existence in time (and hence also of its determinability in time), and that is more than to be conscious merely of my presentation.” – Immanuel Kant