104 ADAPTATION AND PROGRESS 
Moreover he was familiar with the teachings of the classical 
economists ‘“ that labor is the source of value, but that of this 
value the laborer obtains for himself merely a subsistence wage,! 
the surplus being appropriated by the exploiting capitalist.’ ? 
Such theories gave him the background for his fundamental doc- 
trine that this theft of the surplus-value of labor is the fountain- 
head of all social inequality and of the modern industrial system 
with its exploitation of the laboring class. With these premises 
his conclusion was inevitable: The supreme need that the workers 
of each nation and ultimately of all nations should unite in a class- 
conscious revolution against their exploiters and secure the 
socialization of all wealth, all of which was the product of social 
labor.’ 
Of special interest for our purpose is Marx’s philosophy of his- 
tory which has come to be known as “ economic determinism.” 
This principle, set forth in the Manifesto of the Communist Party 
in 1848, drawn up jointly by Marx and Engels is stated by the 
latter in the introduction to the second edition to mean 
That in every historical epoch, the prevailing mode of economic produc- 
tion and exchange, and the social organization necessarily following from it, 
form the basis upon which is built up, and from which alone can be explained, 
the political and intellectual history of that epoch; that consequently the 
whole history of mankind (since the dissolution of primitive tribal society, 
holding land in common ownership) has been a history of class struggles, 
contests between exploiting and exploited, ruling and oppressed classes. 
Though in this quotation all the emphasis is on methods of 
production and exchange, the social forces were not always so 
narrowly limited by Marx and Engels,‘ nor are they so limited by 
leading exponents of this philosophy today, but include all human 
endeavor to satisfy the fundamental needs of life. In other 
words, as W. J. Ghent phrases it: 
The economic interpretation of history is the doctrine that the relations of 
men to one another in the matter of making a living are the main under- 
lying causes of men’s habits of thought and feeling, their notions of right, 
1 Capital, pp. 119, 150 f., ch. XVII. 
2 Kirkup, op. cit., p. 154; cf. Capital, p. 517. 
3 Manifesto (1898) p. 33, Capital, pp. 621, 788 f. 
4 Cf. Walling, The Larger Aspects of Socialism, p. 379. 
