It would be out of place, here, to try to write the interpretation of that marvellous and difficult piece of dialectic--the _Wissenschaftslehre_;--a theme to which Fichte returned again and again up to his death, ever modifying details, selecting new modes of exposition, and gradually, perhaps, changing the centre of gravity of his system. It will be sufficient to note the two purposes which it keeps in view. On the one hand it is a systematic theory of the categories. It begins, as we have seen, with the three co-ordinates of all reflection,--identity, difference, and reason why; it proceeds to the co-relative principles of activity and passivity; to condition, quantity, &c. And its work is to show how these forms naturally emerge in the recurrent antithesis which arises in consciousness, and how again they are brought together by the overmastering Absolute thesis into a synthesis, from which the same process re-appears. How much this corresponds in general conception to the Hegelian Logic is obvious, and Fichte has the merit of the original suggestion. With this however he conjoins--what Hegel has relegated to his Psychology--an evolutional or developmental theory of the mental powers. We have already seen how sensation is forced by the latent intelligence to rise into perception (_Anschauung_): the line of psychological development is carried on by Fichte through imagination to understanding and reason. Hegel's work is far more complete, definite, and detailed: but that need not keep us from giving due homage to the suggestive sketch of the originator of the conception[9]. But the theoretical consciousness is not all; and as we already know, the practical Ego is supreme over it. In it lies the key to the mystery of the stimulus--the shock from the unknown--which awakened the activity of the Ego. The non-ego is only a mass of resistance created by the Ego so that it may be active; only a stepping-stone on which it may walk; a spring-board from which it may bound. Only so much reality has the non-ego; the reality of something which may be shaped, made, made use of. Call the something which the stimulus (_Anstoss_) pre-supposes, the thing-in-itself (after Kant): and if you ask How are things-in-themselves constituted, you get from the _Wissenschaftslehre_ the answer: 'They are as we should make them[10],' Or, as it is said in another place: 'My world is--object and sphere of my duties and absolutely nothing else[11]:' if you ask whether there is really such a world, the only sound reply I can give is: 'I have certainly and truthfully these definite duties, which take the form of duties _towards_ such, and _in_ such, objects; and it is only in a world such as I there represent and not elsewhere that I can perform these duties which I cannot conceive otherwise,'