The Social Origins Of The Brussels Propertied Middle-Classes Of 1914: The fact of having the disposal of all means of power of the establishment is not the only reason for the survival of the middle-class society. The flexible character of capitalism is attributable in the first place to a chance built-in mutation mechanism of the executive groups. Renewed executive groups adapt themselves to the contemporary circumstances more easily than a hereditary class, thus protecting the system from an undermining of its power. This became apparent from an investigation into the social origins of the Brussels propertied middle-classes of 1914. As a sample-group we selected those eligible for the senate of 1914 who were born in Brussels. This group fell apart into three clear-cut subdivisions. The first subdivision was composed of 22 eligibles or 29.33 % and entered the top-stratum in the period between 1880-1914. Sprung from lower middle-class, these people were pre-eminently active as wholesalers and manufacturers. In the opinion of society they were the capitalists; they came into direct contact with the labourers. Materially they had reached the top and all their endeavours aimed at consolidating a substantial financial basis, the prerequisite for integration into the top. But they did not yet belong to the decision-making élite. Their situation was still too unstable. The second subdivision, the upper middle-class, was composed of 20 eligibles or 26.66 %. Their parents had entered the top-stratum in the period between 1850 and 1880. They directed their full attention to this integration-process. The results were still limited, owing to a timid application of the appropriate means : acting as a director of limited liability companies, as a political mandatary, finding a spouse whose family was related to the decision making élite. The third subdivision, the financial aristocracy, was composed of 33 persons, or 43.99 %. About or before 1850 their families already belonged to the top-stratum. Their integration into the group of the decision-making élite had been completed. They were directors of numerous limited liability companies and cumulated mandates in all sectors of social life. They were married into families with wide branchings in the leading circles. The latter phenomenon was so strongly marked in subdivision III that, in spite of the local limitation of the group, they formed not only a unity on the grounds of an identical evolution-pattern, but also a unity on the basis of family-relationship. This decision-making élite of 1914 was no longer the one of the first half of the 19th century. The latter stood up for values that were progressive for the first part of the 19th century, but no longer so more for the end of it. Economic freedom could offer more to the enterprising captain of finance, manufacturer and wholesaler. The people of the third subdivision, who still lived in the shade of the first generation about the middle of the century, were very keenly aware of that fact. The period between 1850 and 1880 witnessed the great mutation. With the new economic expansion the second generation dashed past the first, carrying along a limited part of the former élite that had not failed to see the course of the new development.