Herbert Spencer (1820–1903) was one of the most popular and influential 19th-century sociologists. It is estimated that he sold one million books in his lifetime, far more than any other sociologist at the time.

The Second Great Transformation? Capitalism at the End of the Twentieth CenturyDynamic Sociology—Or Applied social science as based upon statical sociology and the less complex sciences

Contemporary sociological theory retains traces of each of these traditions and they are by no means mutually exclusive.

Functionalist thought, from Comte onwards, has looked particularly towards biology as the science providing the closest and most compatible model for social science. Biology has been taken to provide a guide to conceptualizing the structure and the function of social systems and to analyzing processes of evolution via mechanisms of adaptation. Functionalism strongly emphasizes the pre-eminence of the social world over its individual parts (i.e. its constituent actors, human subjects).

To aim for a civilization beyond that made possible by the nexus of the surrounding environment will result in unloosing sickness into the very society we live in. Collective activity cannot be encouraged beyond the point set by the condition of the social organism without undermining health.

The history of all hitherto existing society is the history of class struggles. Freeman and slave, patrician and plebeian, lord and serf, guild-master and journeyman, in a word, oppressor and oppressed, stood in constant opposition to one another, carried on an uninterrupted, now hidden, now open fight, a fight that each time ended, either in a revolutionary re-constitution of society at large, or in the common ruin of the contending classes.

Lastly, sociological theory often grapples with the problem of integrating or transcending the divide between micro, meso, and macro-scale social phenomena, which is a subset of all three central problems.

The latter concern with scientific knowledge results from the fact that a sociologist is part of the very object they seek to explain, as Bourdieu explains:

How can the sociologist effect in practice this radical doubting which is indispensable for bracketing all the presuppositions inherent in the fact that she is a social being, that she is therefore socialised and led to feel "like a fish in water" within that social world whose structures she has internalised? How can she prevent the social world itself from carrying out the construction of the object, in a sense, through her, through these unself-conscious operations or operations unaware of themselves of which she is the apparent subject

Pierre Bourdieu, "The Problem of Reflexive Sociology", An Invitation to Reflexive Sociology (1992), p. 235

The following list of research methods is neither exclusive nor exhaustive: