In this chapter Weizenbaum states that man has been enabled to transform his physical environment by machines and he asserts that "the machines of man have strongly determined his very understanding of his world and hence of himself." Man’s tools are pedagogical instruments and they are used to help fashion man’s imaginative reconstruction of the world. A tool is a "vehicle for instructing men in other times and places in culturally acquired modes of thought and action." The tool is not just a device, it is an agent for change. Many tools are a functional addition to the human body, a prosthesis. Modern science arose when man transformed nature and his perception of reality. But not all machines act as a prosthesis. The clock is one example. Man’s perception of time used to be regulated by natural events, such as the rising and setting of the sun, or hunger, which would indicate it was time to eat. The clock, however, once set in motion, functioned autonomously, like the planetary system, and acted to regulate human existence. So an autonomous machine now regulated human activity in such a way that direct experiences which had been the foundation of the old reality were now replaced by an abstract model, the clock, which constituted the new reality.

One of the hallmarks of modern science was this rejection of direct experience. Gradually numbers, in the form of quantifiable measurements, came to represent reality and these numbers became indispensable as legitimate representations of reality in common wisdom. These numbers came to mediate between man and nature, alienating man from nature. Then came the computer, which came to be regarded as an indispensable tool. In an increasingly complex world many people do not see life without computers as a viable option to meet the complex demands of modern life. We believe we have reached the limits of human competence, beyond which only computers are capable of handling the demands made upon us. These demands have been made upon us in such diverse areas of military defense, the production of automobiles and the administration of social services. But Weizenbaum believes that in regard to the latter computers may have perpetuated institutions that were in need of social and political innovation. It may be that these innovations did not take place because computers saved institutions that may have been improved by social and political innovation.

Computers have done more than just invent new and better ways of doing old tasks. But computers have created new problems that may not necessarily be dealing with the fundamental tasks they are supposed to solve. There may be a particular technique that requires an enormous amount of computation but only a limited amount of computation can be applied to it. Computational limitations may be used to explain a failure of the technique and so great effort is expended to overcome the computational limitations. Great efforts are directed at "computerizing" this technique. When finally this problem is overcome those who overcame it may feel that a great deal has been done and learned but the original problem may be no closer to being solved than before.

The very possibility of acting in older ways may be eliminated by new technology. This may or may not be irreversible according to Weizenbaum. In order to maintain control and not let computers take over decision making, people may take computer processed information and make their own decisions about what to do with that information. However, a computing system that permits the asking of only certain kinds of questions or only accepts certain kinds of data and a system that is not fully comprehended by those who rely on it, is a system that has effectively closed doors that were previously open before the system came into use.