Obligations are called for certain active positive actions. Seldom - passive function which does not settle object of the obligation, and usually acts as result or addition to positive actions of his subjects. For example, the passive duty of the lessor not to prevent the employer to use property is a consequence of the positive action for transfer of property which is already earlier made by it in use or possession.
From the point of view of contents of obligations, especially from their definiteness, allocate different types of obligations. So, for example, obligations can be simple and alternative depending on