Dual twins in architecture have been widely spread since the middle 20th century in various parts of the world; however, the unclear and comprehensive view about the nature and reasons of the emergence of such phenomena is still not established. The current study attempts to determine the nature and reasons of the emergence of such phenomena clearly and comprehensively. In order to examine the theoretical background of this phenomena, concept of twins in language, philosophy, biological and medical sciences is reviewed in addition to examining principles of dual architectural and artistic composition and the priors of dual twins in history of architecture. Thus, the two hypothesis of the study are formed where the first states that dual twins are either identical or fraternal, related or not related materially with each other. The second indicates that unity of design is the reason behind the emergence of dual twins leading to aesthetics, integrity within the urban context.
The study has made a deductive survey of 27 of dual twin buildings around the world. The study concluded that both the hypothesis are largely met but not absolutely. There are identical and fraternal twins but not materially related with each other and characterize by a complete structural and functional independence with their visual interrelation forming both of them as one dual composition. Concepts of architectural composition aiming at breaking monotony and presenting the new were the most influential in the emergence of dual twins in architecture in addition to other functional, rational, urban and environmental causes.
Keywords: dual twins - dualism.