In this article, which comprises the eighth chapter of Studies in Ethnomethodology, Harold Garfinkel considers the problem of studying the rationality of everyday activities. According to Garfinkel, so far sociologists used the ideal of scientific rationality as the main criterion for determining the presence or absence of rationality in daily activities. However, according to Garfinkel, the scientific rationalities, in fact, occur as stable properties of actions and as sanctionable ideals only in the case of actions governed by the attitude of scientific theorizing. By contrast, actions governed by the attitude of daily life are marked by the specific absence of these rationalities either as stable properties or as sanctionable ideals. It follows that instead of the properties of rationality being treated as a methodological principle for interpreting activity, they are to be treated only as empirically problematical material. They would have the status only of data and would have to be accounted for in the same way that the more familiar properties of conduct are accounted for. The scientific rationalities are neither stable features nor sanctionable ideals of daily routines, and any attempt to stabilize these properties or to enforce conformity to them in the conduct of everyday affairs will magnify the senseless character of a person’s behavioral environment and multiply the disorganized features of the system of interaction.