Concept
theory
A systematic set of ideas that helps make sense of a phenomenon, explain it, predict a consequence and guide action; in the strict sense, connected propositions from which observed regularities can be derived.
In its broadest sense, a theory is any systematic set of ideas that helps make sense of a phenomenon, guide action or predict a consequence (McQuail). The strict sense is Merton’s: a set of logically connected propositions from which observed regularities can be derived. A theory is more than a single hypothesis or an isolated empirical generalisation: it contains the set of assumptions from which the generalisations themselves are derived.
That is why it matters to tell theory apart from hypothesis, model, paradigm and common sense. Details in the What Is a Theory? Paradigms and Classifications lesson.
Example
The “theory of relative deprivation”: people compare themselves with others they see as similar, so under some conditions those who suffered a bigger loss may feel less deprived (Merton 1949).