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.
The pure ego is inferred from the fact that the non-ego is realized only in the act of the ego in positing it.
(I) This must exclude everything negative; for non-A sublates instead of positing, and is not absolute, but relative to A.