It is quite a practical method to set a limit for one's investigations, not to fly into clouds, not to undertake anything that cannot be accomplished. Yet you must not forget that practical boundaries are not theoretical boundaries, that they are not invariable boundaries for you, or for others. Although you cannot fly to heaven and will give up the idea of flying machines from considerations of practical expediency, yet you will not wish to deny to man the theoretical freedom of infinite striving even in the matter of airships, and you will not be so small as to give up the idea of the capacity for our race for metaphysical, or in other words, infinite development. FOOTNOTE: [3] In the sense of: mental and physical world embracing, all-embracing.--Editor. FOURTH LETTER Dear Eugene: In my first letter I acquainted you with my purpose, in the second I lifted the subject on my finger tips, so to say, to show it for a brief moment; in the third I showed that its color had inevitably a religious shade. Now, to continue, permit me to introduce another point to your consideration. The great cause of the working class has hitherto always been the beast of burden of a small and exclusive minority. This is most evident in the slave states of antiquity, in Egypt, Greece, Rome. Likewise in the feudal and guild systems of the middle ages the oppression of the mass of the people is sufficiently apparent. At present this condition of things is more visible in Eastern Europe, in Russia, Turkey, Bulgaria, Hungary, Eastern Prussia, etc., than in the industrial countries of the West. In the United States of America it is most obscured, so that there the people hardly realize their enslaved condition. In America, many of the upper ten thousand have made their way from the bottom up, and it happens more frequently than in Europe that the captains of industry laid their foundation by hard work. The shortsighted observers then easily forget out of sympathy for the hard beginning that there is sharper's practice at the end, and they indulge in the idle hope that every hard working beast of burden might transform itself into a happy millionaire by thrift and smartness. You will probably ask: What has that to do with logic or the art of reasoning? Patience! You will admit that the emancipation of the nations from beastly toil, misery and suffering is the highest goal of the human mind. Nor will you deny that the thought is the most essential instrument for reaching this high goal. The accomplishments of thought are visible in the results of civilization. The proletariat of the present, also that of Russia, Turkey, East Prussia, participates in these accomplishments of thought. It participates not alone in the sense that its brains are better educated and cultured, but also that its food, clothing, and shelter have become more civilized through the progressive deeds of intellect.