A scientific theory is a well-substantiated explanation of some aspect of the natural world that is acquired through the scientific method and repeatedly tested and confirmed through observation and experimentation.
Social theories are frameworks of empirical evidence used to study and interpret social phenomena. As a tool used by social scientists, social theories relate to historical debates over the most valid and reliable methodologies, as well as the primacy of either structure or agency.
"Theory" as it is mostly used in academia today is an outgrowth or consequence of critical theory, which emerged out of the Marxist tradition and was developed by social scientists and philosophers in Germany during the mid-twentieth century. It is a type of theory that aims to critique society, social structures, and systems of power, and in doing so, to foster egalitarian social change.
Literary theory in a strict sense is the systematic study of the nature of literature and of the methods for analyzing literature. Historically literary scholarship since the 19th century often includes - in addition to, or even instead of literary theory in the strict sense – social or critical theories which pertain to the way humans interpret meaning. In humanities in modern academia, the word "theory" has become an umbrella term for a variety of scholarly approaches to reading texts and many of these approaches are informed by various strands of Continental philosophy and sociology.
Literary criticism is the study, evaluation, and interpretation of literature. Modern literary criticism is often influenced by literary theory, which is the philosophical discussion of literature's goals and methods. Though the two activities are closely related, literary critics are not always, and have not always been, theorists. Literary theory in a strict sense is the systematic study of the nature of literature and of the methods for analyzing literature.