In space and time utopias one line of thought requires the capability of classifying and distinguishing. In order that it be fruitful and not purely theoretical a flexible definition of boundaries is needed so that the fuzziness of actual life may be preserved. Mathematics supplies some consistent definitions that can be tailored in order to correspond to real experience. In the paper some critical examples are shown, that prove that the concept of boundary is very sophisticated and by no means completely intuitive. Examples of spatial boundaries are given, namely hard boundaries versus distributed boundaries. The section on time boundaries is founded on de Saussure’s distinction between synchrony and diacrony. Total isocronies seldom happen but psycologically some form of isocrony is constantly perceived. The reconstruction of past very often must follow an erratic system of comparisons, similar in some ways to CPM technique of project management of operation research. Boundaries therefore become very fuzzy and very subjective, as literature and psychology show.
