But here I may be allowed to make a remark. Labriola is also waging war with Sorel: his book _Discorrendo_, etc., arising out of a series of friendly letters to Sorel, which I undertook to edit in Italy, is published in French with an appendix directed against me, and a preface directed against Sorel. The ground of the quarrel is especially in connection with the so-called _crisis in Marxism_. Now if the _crisis in Marxism_ be understood as the assertion of the need for a revision and correction of the scientific ideas, of the historical beliefs, of the material of observed facts, which are current in Marxian literature, well and good: in such a crisis I too believe. If it means also a change in the programmes and practical methods, I neither agree nor disagree, having never concerned myself with the subject in dispute. If the danger is really existent the apprehension of which seems to obsess and disturb Labriola, that a crisis in Marxism of whatever kind, or the commencement of it, may be neutralised by those to whose interest it is to lead astray and scatter the labour movement, then _provideant consules_. But whether there be crisis or no crisis, whether purely scientific or also practical, whether apprehensions are well-founded or imagined and exaggerated, all these things have no connection with the questions raised by me, which relate to the erroneousness of this or that theoretical or historical statement of Marxism, and the way in which this or that must be understood in order to be regarded as true. This is my standpoint and on this ground alone I admit discussion. I may be mistaken, but this must be proved to me. But if, on the contrary, the only answer vouchsafed to me is that the crisis in Marxism results from the international reaction, of which ingenious critics are taking advantage, I shall be left it is true, somewhat bewildered; but I shall not on this account be convinced that the theory of value is true, in the burlesque sense, for example, in which it is expounded by Stern in his well-known propagandist booklet. Sorel at first supposes,[83] wittily enough, that Marx had built up different economic spheres, the first of which (that of labour-value) is the simplest; the second, including the phenomenon of an average rate of profit, and the creation of cost of production, is more complex, and the third, in which is observed the effect of rent of land, is still more complex. In passing from the simple to the more complex sphere, we should find again the laws of the preceding one, modified by the new data introduced, which would have given rise to new phenomena.