How this act of op-positing is possible and necessary, only becomes clear in the practical philosophy, and even there the inherent difficulty leads to a higher view.
But in consciousness there is equally given a primitive act of op-positing, or contra-positing, formally distinct from the act of position, but materially determined, in so far as what is op-posited must be the negative of that which was posited.
If the ego be pure activity, free activity, it can only become aware of itself by positing some limit.
This construction, or self-determination, is what Fichte called positing (setzen).
Hence he united theoretical and practical reason, which Kant had separated, and both with will, which Kant had distinguished; for he held that the Ego, in positing the non-Ego, posits both its own limit and its own means to the end, duty, by its activity of thinking which requires will.