Theory is a base for all scientific disciplines. Theorizing is an important branch in architecture too. There are a little reference that tries to define theory and show the differences between theory in architecture and theory in other disciplines. This article aimed to show the characteristics of architectural theory. At first we try to review different books and articles which are written on architectural theory. There are many books on this title, but most of them don’t pay attention to the nature of theory in architecture. There are few books on architectural theory that present a comprehensive view of the field and none that review the essence of theory in architecture. We can find two categories of the works on architectural theory, the works that try to define theory especially in architecture, and the works that try to theorizing a new idea in architecture, particular or generic themes. The second part is finding the characteristic of architectural theory. The meaning of this word is surveyed through etymological references and dictionaries. It can help us to find out the origins, history and changing meaning of theory, so we can follow the changes of the meaning through the centuries till now. Starting from its origins in theoria, theory has become much more developed in meaning. It has never lost its basic characteristic as a removed and systematic accounting of an object. It shows us that logical rigor is the base of every theory so we categorize theories according to this characteristic and we can develop operational definitions of them. Theory in general has certain attributes, but it is difficult or perhaps impossible to conceive of it as one conceptually homogeneous domain. As David Wang in his book on the title of “architectural research methods” said the difficulty reflected the complex unity that is human mind, with its ability to receive and explain empirical experience in multiple ways and simultaneously. There are many kind of theory, positive versus normative theory, different scales of theory, polemical versus scientific theory and so on. But in this article theories are categorized according to their rigor. We address three kinds of theories: logical based theory, experimental based theory, and semi-theory, then similarity or differences between these theories are shown. Then we try to clarify situation of them in architecture, and define the characteristics, domains, and ability of these theories especially in architecture. The theories of aesthetic and philosophy of architecture usually are logical based. Deduction is the method for this kind of theories. Typology, styles of architecture and case studies researches in architecture usually use experimental based theories. They use induction as method. The third category is semi-theory. Semi-theories is the most popular theories in art, architecture and social sciences. The theories which have a kind of prediction, suggestion, description of best architecture and architect’s viewpoints are semi-theory. Persuasion is the method used in this kind of theories. The approach of two first categories of theory is positive, but semi-theory is based on normative approach.