By this appeal to experience and by this rejection of all metaphysical intrusion, I place myself in a position to meet the objection which you bring forward to my conception of economic data. You think that the ambiguity of the term _value_ comes from this, that it denotes a very complex fact, a collection of facts included under a single word. For me, on the contrary, the difficulty in it arises from its denoting a very simple fact, a _summum genus_, _i.e._ the fact of the very _activity_ of man. Activity is value. For us nothing is valuable except what is an effort of imagination, of thought, of will, of our activity in any of its forms. As Kant said that there was nothing in the universe that could be called _good_ except the _good will_; so, if we generalise, it may be said that there is nothing in the universe that is valuable, except the _value of human activity_. Of value as of activity you cannot demand a so-called genetic definition. The simple and the original is genetically indefinable. Value is observed immediately in ourselves, in our consciousness.[98] This observation shows us also that the _summum genus_ 'value,' or 'mental activity' gives place to irreducible forms, which are in the first instance those of theoretical activity and practical activity, of theoretical values and practical values. But what does _practical_ mean?--you now ask me. I believe that I have already answered by explaining that the theoretical is everything which is a work of _contemplation_, and the practical everything that is the work of _will_. Is will an obscure term? We may rather call the terms _light_, _warmth_ and so on, obscure; not that of _will_. What will is, I know well. I find myself face to face with it throughout my life as a man. Even in writing this letter, today, in a room in an inn, and in shaking off the laziness of country life, I have _willed_; and if I have delayed the answer for two months, it is because I have been so feeble as not to know how to _will_.