Technosystem should be read as a attempt to link up several different traditions of social thought in an innovative theory of modernity. The big question to which Technosystem is addressed is the difference between modern society and all earlier forms of society. The answer is the place of rationality in social life. Reason is a mental faculty, equally present in the human mind throughout all of history and indeed of pre-history. But only in modern society are the major social institutions organized as rational systems. Where custom and tradition used to guide most social decisions, today we look up the answers to our questions in user’s manuals and the texts of the various technical disciplines that preside over our lives.At the beginning of the 20th century, philosophers and sociologists attempted to understand the difference between reasoned grounds for belief and rational procedures of social organization. A scientific theory is rational in the first sense if it is based on good evidence and sound reasoning. In that case we have reason to believe it. A bureaucratic system is rational in the second sense if it follows its own well formulated rules. As good citizens or employees we are expected to obey it even if those rules are not based on a scientific understanding of the world.There is more: social rationality masks many non-rational influences on social decisions. For example, unlike bureaucracy, technology must be based on valid knowledge. That knowledge satisfies the first definition of rationality. It is usually codified in a technical discipline such as engineering. But since there are many ways to apply the technical disciplines in any particular case, there are always design decisions that depend on other sources such as economic, political, aesthetic, or traditional notions. Ordinary individuals weigh on the decisions through various means such as markets, regulation, hacking and social protest. The resulting technologies appear perfectly rational even though many other motives have played a role in their design.In the end we get technologies that embody values as well as knowledge but this is a hidden, unconscious aspect of the technical environment. Similarly, bureaucracies and markets justify themselves as rational even though they embody many social forces that have no basis in knowledge. The veil of rationality covers these other influences and makes social criticism difficult. Rationality has become the dominant ideology. Technosystem is therefore an argument for a new kind of ideology critique adapted to the rational society.