I might enlarge further on this distinction and show how it has an analogy in the sphere of theoretical activity, where the relation of economics to ethics is repeated in the relation of æsthetics to logic. And I might point out the reason why scientific and æsthetic productions cannot be subjects of economic science, _i.e._ are not economic products. The reason given, in this connection, by Professor Ehrenfels, is, to say the least of it, curious: he remarks that: 'the relations of value upon which the data of logic and æsthetics rest, are so simple that they do not demand a special economic theory.' It should not be difficult to see that logical and æsthetic values are theoretical and not practical values, whereas economic value is a practical value, and that it is impossible to unite an _economics_ of the _theoretical_ as such. When, some years ago, the lamented Mazzola sent me the introduction in which he had discussed _Economics_ and _Art_, I had occasion to write to him and afterwards to say to him by word of mouth, that much more fundamental relations might be discovered between the two groups of phenomena; and he urged me to expound my observations and inquiries. This I have done in the essay on _Estetica_, referred to above. I am sorry to be obliged to _refer_ so many times in writing to you and to the public. But here the need for brevity and clearness constrains me. This, then, is a rapid statement of how I arrive at the definition of the data of economics, which I should like to see at the beginning of every economic treatise. _The data of economics are the practical activities of men in so far as they are considered as such, independent of any moral or immoral determination._ Granted this definition, and it will be seen also that the concept of _utility_, or of _value_ or of _ofelimity_, is nothing but the economic action itself, _in so far as it is rightly managed_, _i.e._ in so far as it is really economic. In the same way as _the true_ is _thinking_ activity itself, and _the good_ is _moral_ activity itself. And to speak of things (physical objects) as having or not having value, will appear simply a metaphorical usage to express those _causes which we think efficacious to produce the effects_ which we _desire_, and which are therefore our _ends_. _A_ is worth _b_, the value of _a_ is _b_, does not mean (the economists of the new school knew it well) _a=b_; nor even as is said _a>b_; but that _a_ has _value_ for us, and _b_ has not. And value--as you know--exists only at _the moment of exchange_, _i.e._ of _choice_.