In order to discover the cause of the outbursts of novae, a study of the physical processes taking place in novae during such explosions is not sufficient. A number of other, and no less important, properties and peculiarities of novae must also be investigated. Such properties are, for instance: the absolute magnitudes at light maximum and minimum, the temperatures, the light curves and their variations, the position of the novae on the Hertzsprung-Russell diagram, their spatial distribution in the Galaxy, and the mutual relations between the novae and other objects of similar nature (such as the recurrent novae, super-novae, nova-like stars, and the nuclei of planetary nebulae). A hypothesis of the origin of the outbursts of novae should be founded upon all these data as well as the other properties of novae.