At first, Durkheim seems to rule out any attempt to justify or invalidate morality, including morality in a society. In Sociology and Philosophy, he cautiously states: Moral reality, like all reality, can be studied from two different points of view. One can seek to know and understand it; or one can propose to judge it. The first of these problems, which is theoretical, must necessarily precede the second, and it is the only one that will be dealt with here ².

The point here, then, would be to understand morality, not to judge it; but Durkheim is going to move imperceptibly from one point of view to the other, as we shall see.

Durkheim's first aim was to show that a moral fact is a social fact. To do this, he relies on the idea that an act can never be called moral if its sole object is the interest of the individual or of other individuals. Morality can only have as its objective the group formed by a plurality of associated individuals, i.e. society, understood as a personality that is qualitatively different from the individual personalities that make it up. As a result, Morality begins where attachment to any group begins ².

Above all, a moral fact is a social fact because it corresponds perfectly to Durkheim's definition of a social fact in the Rules of Sociological Method. In this work, Durkheim sought to give sociology the status of an autonomous discipline, irreducible to the disciplines to which it was being reduced: psychology and biology.

At that time, it was thought that since society was made up of individuals, social rules were derived from the minds of individuals, and that ultimately the psychological analysis of the human mind could provide the content of sociology, which was thus deprived of any consistency of its own, to the benefit of psychology.
It was also thought that society was analogous to a biological organism, made up of individuals comparable to the cells of that organism. This biological metaphor meant that sociology was deprived of any consistency of its own, its content and methods having to be those of biology.

Against this, Durkheim tries to show that there is a proper definition of social fact, distinct from biologistic or psychologising definitions of it. Durkheim points out that even if I respect the social rules in force, i.e. my individual mind is in agreement with them, these rules do not derive from my mind (i.e. are not psychological) but are imposed on me externally, whether I like it or not. These rules exist before us and outside us, and are endowed with an imperative and coercive power by virtue of which [they] impose themselves on us whether we like it or not. They cannot therefore be derived from my mind, but are imposed on it, which is why sociology does not derive from psychology.

This leads Durkheim to propose this conclusion: a fact is social because it is obligatory: A social fact is recognisable by the power of external coercion which it exercises or is likely to exercise over individuals; and the presence of this power is in turn recognisable by the existence of some specific sanction or by the resistance which the fact opposes to any individual undertaking which tends to do it violence ³.

A moral fact is therefore, profoundly, a social fact, which falls within the remit of sociology, because it is obligatory. The question that now arises is: can sociology, as a science of social facts, provide a foundation for the social fact that is morality? Does sociology hold the answer to the problem of the foundation of morality?
Durkheim's answer to this question is in the affirmative: one moral rule will be justified because social causes favoured its emergence and maintenance; another will be abandoned because the social conditions that led to its adoption have disappeared, and it is no more than a baseless survival of a vanished social state:
The awareness that society acquires of itself in and through opinion may be inadequate to the underlying reality. It may be that opinion is full of survivals, lagging behind the real state of society [or that] certain principles of existing morality are, for a time, rejected in the unconscious". Fortunately, "the science of morality makes it possible to rectify these errors ⁴.

Durkheim deduces from this way of founding a particular moral rule the foundation of morality in general: It will be maintained that no morality can ever be desired other than that which is demanded by the social state of the time. To want any morality other than that which is implicit in the nature of society is to deny it, and consequently to deny oneself ⁵.

1. Sociology and philosophy, chap. II
2. Ibid.
3. Rules of sociological method, chap. I
4. Sociology and philosophy, chap. II
5. Ibid.