Vida Rahiminezhad That is an interesting question. Unlike other fields of the scientific spectrum, appraoch and theory are generally used interchangeably. An approach is more general whereas a theory is a subsection that is more specific. I checked some sources but every source names different numbers of approaches. I think the general classifications such as Formalism, Structuralism, Post-Structuralism, Psychoanalytic are approaches whereas Semiotics, Marxism, Feminism, Freudian and Jungian are literary theories. As I said, lots of sources mix up these two and many people use both terms.

Vida Rahiminezhad Actually this could be a problematic issue. I know a distinguished professor claiming there is an "approach problem" in literature.

A theory is a framework for understanding relationships between observable facts. A theory is the body of ideas and methods. An approach is a practical way of dealing with a situation, or the way we might do a theory

“Literary theory” is the body of ideas and methods used in the practical reading of literature. By literary theory we refer not to the meaning of a work of literature but to the theories that reveal what literature can mean. Literary theory is a description of the underlying principles, or the tools, by which we attempt to understand literature. All literary interpretation draws on a basis in theory but can serve as a justification for very different kinds of critical activity. It is literary theory that formulates the relationship between author and work; literary theory develops the significance of race, class, and gender for literary study, both from the standpoint of the biography of the author and an analysis of their thematic presence within texts. Literary theory offers varying approaches for understanding the role of historical context in interpretation as well as the relevance of linguistic and unconscious elements of the text. Literary theorists trace the history and evolution of the different genres—narrative, dramatic, lyric—in addition to the more recent emergence of the novel and the short story, while also investigating the importance of formal elements of literary structure. Lastly, literary theory in recent years has sought to explain the degree to which the text is more the product of a culture than an individual author and in turn how those texts help to create the culture.

For a detailed account of modern literary theories, I suggest:

Raman Selden, A Reader's Guide to Contemporary Literary Theory, Routledge.

Literary criticism, after all, is not the antithesis of literary history, nor is it something different; On the contrary, it is the correct introduction to the history of literature, and no real history of literature can take place, without a real literary criticism movement of texts as a whole and distinctions in the light of a systematic plan, and that the movement of real literary history, as well as the movement of the history of literary criticism cannot be Either of them is properly accomplished in isolation from a systematic movement to read all texts, analysis, interpretation and evaluation from different levels. Perhaps the true history of literature and criticism is the greatest achievement that true serious critics can make.

lierature gives us the possibility of criticism, which is to talk and talk about it, neither Hegelian adverse thesis or complete different antithesis, thus it can give us retale it... and even true history doesn't exist in any time to stop to tell tales, stories, fairy tales, gossips, gists, old-wives and endless affairs plenty of falsehoods...

Literature, by convention, deals with human experience and conditions. These human conditions and experience are left open to different interpretations by readers and critics. For a valid and scholarly interpretation, critics are by convention required to base their interpretation on certain theoretical assumptions. These assumptions are the approaches. While the theories are the lenses with which the critic view the text. In a nutshell, the theory is the philosophical foundation of the approach. Thank you.

mostly we agree but in political literature demanding criticism all isn't conventions, there are established facts, claims and something whether what they are saying is true and told...

The different approaches of literary theory are like the rules for implementing it in your analysis. Thus, the approaches of literary theory are being taken forward to take forward in the way if literary criticism.

Suppose you are dealing with the textual reading of the text. You may give a quick read of it. But that doesn't mean that you have done justice to it. There may be certain factors which might have struck your mind like portrayal of women, authors nativity, time period in which it has been written, is the author biased enough... etc. For these all things you need literary theories to analyse the way which struck your mind. Whether feminist theory, Marxist theory or any other theory. This will help you to approach criticism in a better light

the invention or design of works hs their own way to exist, we put the rules to work out the arbitrarily direction to understand and classify it; to suppose one's way to read, this moment depends on time, purpose and aim so as to follow rules because all minds are not interested to be framed by rules, for instance Flaubert's Madame Bovary; Lovecraft; Wordsworth or Keats....

Approaches are perspectives from which literature or literary works could be evaluated. These may include sociological, psychological or formalistic approach

Interesting!

Literary approaches feature the background, context and/or period relating to either the text, the author or both. It is well-known that literary writings respond to the author's feelings and expressions towards a particular phenomenon. Hence, we have historical, gender, cultural and psychologial approaches among others.

Literary theories, on the other hand, are tools that are used to investigate and analyse the validity of a research problem. For instance, if a research study investigates identity in a specific society, the Marxism Theory of Literature may come in handy in order to understand how one's identity can be downgraded due to various factors relating to economic and political struggles.

I must say, it is common to find others using both terms interchangeably.

Surely, the major style of the work under-investigation is what defines ,mostly, the method you would follow