Literary lenses (which are more formally called Schools of Criticism) focus on one basic principle:
Different readers read the same text differently.
Knowing how different groups of readers read a text can illuminate deeper meaning and new interpretations. Literary lenses also work for literally ANY TEXT, even one as simple as "Cinderella." Though there are many literary theories, what follows are the most common ones.
SOCIETAL MIRRORS are criticisms that reflect society. Societal mirrors focus on the idea of The Other, a term for a person in society with little power or agency (the ability to change their circumstances). Those with agency are known as the privileged group, as they have access to resources that The Other does not. Some members of the privileged group actively work toward this inequality, while most members of the privileged group have social blindness--they do not willfully wish to subjugate others, but because their privilege is normal, they do not perceive or understand the struggles of The Other. There are six societal mirrors: Marxism, postcolonialism, feminism, queer theory, ecocriticism, and affliction theory.
Marxism explores power struggles based on societal classes. Marxism is based on the writings of Karl Marx (duh), specifically the ideas put forward in his Communist Manifesto. Essentially, Marxists believe that all of history is a struggle for resources (which they call dialectical materialism). This leads to two groups: the bourgeois (who have resources) and the proletariat (have-nots). This class struggle leads to all conflict, and causes feelings of alienation for those in the proletariat who must take any work to survive: alienation from one's labor, from others, and from a sense of purpose.
Postcolonialism, which is associated with critical race theory, focuses on the cultural influences of colonialism and in literature. While post-colonialism tends to conflict resulting from the exploitation of indigenous peoples and their countries by Western nations (think the American slave trade), it examines all conflicts between different cultures or nations when there is a legacy of conquering and subjugation; for example, a postcolonial reading of A Tale of Two Cities could be made by looking at the prejudices between the English and the French. Post-colonialism focuses on the legacy of marginalization, including stereotypes, appropriation, and tribalism.
Feminism explores the power relations and power struggles between men and women. As men hold dominant power in society as part of a patriarchy, men define what it is to be human, thus casting women as the "other." Feminism explores not only the stereotypes and biases men use to define women, but women's own search for her own definition and perspective. While such definition varies (as feminists reject essentialism, or the idea that one definition can apply to all women), all feminists agree that a woman is more than her sex. Feminists instead examine gender, or how society defines what it mean to be a woman. Feminists focus on a woman's agency (her ability to make her own choices), the challenges she faces because of her sex, how she is treated and viewed by men, and how she views herself.
QUEER THEORY AND HOMOSOCIALITY
Whereas feminism explores the dynamics between men and women, queer theory (sometimes called homosociality) explores relations and power struggles between men and other men or women and other women. This covers not just social relationships between members of the same sex (such as friendships, fraternities and sororities of choice, and business partnerships) but same-sex romances as well. Topics of homophobia and transgenderism (when a person of one gender performs as the other gender) are central, as well as societal tests of loyalty to one's "brothers" or "sisters" (think a "bro" code).
Ecocriticism explores the relationships between humanity and the natural world, including animals. In some texts, man and nature exist in harmony; in others, man destroys nature or nature destroys man. Special attention is paid to city life; at times, the city is a symbol of the death of nature, while in other texts, the city is an "urban environment" and takes the role of nature. A focus is also nonhuman characters, which can include monsters, aliens, and robots as well as real animals who play the role of a narrator. As these creatures are not human, an ecocriticist examines how they are subjugated by humans and how they define themselves as not human.
The newest social mirror is affliction theory, also called disability theory. Affliction theory explores characters that have a bodily affliction that impairs them in some way, like Tiresias's blindness or Captain Ahab's peg leg, and asks how the impairment and any disability resulting from it affects the plot and character development of the story. The impairment doesn't have to be permanent (think Beth getting sick in Little Women) and can come from age. Some afflictions may even be seen as blessings instead of impairments (like the titular character of David Copperfield being born with a caul). Affliction theory holds that society reinforces the idea of a perfect flawless body (the normate) and, since none of us are perfect, we all are afflicted in some way.
PERSONAL MIRRORS are criticisms that reflect an individual mind and personality. These criticisms focuses on the ideas of The Self, a term for an individual's definition of their own identity and how this identity makes them different from others. While psychological analysis in the real world is about diagnosing and curing mental or emotional disorders, personal lenses are NOT about putting a character or author on an analyst's couch and examining their kleptomania or schizophrenia. Rather, these mirrors want to depict motivations and subconscious influences on a person's character to better understand their decisions. Psychoanalysis examines the self of the main literary characters, archetypal examines the self of characters that are (duh) archetypes, and authorial examines the self of the (double duh) text's author.
Psychoanalytical literary criticism explores the role of consciousnesses and the unconscious in literature. Based on the work of Sigmund Freud, psychoanalysis examines the psychology of the characters in the text, specifically their wants and repression. Freudian analysis focuses on three layers of personality: the id (wants and impulses), the superego (the moral central concerned about societal rules and judgment), and the ego (which balances the id and superego). Freudian analysis also stresses that there are only two main motivators for all human behavior: eros (desire for love) and thanatos (fear of death).
Archetypal analysis explores the collective unconscious--how all the stories ever written use interconnected images. This is also known as Jungian analysis after psychologist Carl Jung. In his study of dreams, Jung found the same types of images reoccurring in his patients. Inspired by the work of Northrop Frye, Jung named these images archetypes and pronounced that they were universally acknowledged symbols that are innate in all people--one is literally born knowing archetypes. Joseph Campbell built upon Jung's work, claiming all narratives use archetypes and that literature can be seen as a conversation of how to reuse these basic elements in new ways.
Reader response evaluates literature based on the active response of the reader to a text. Authors can't possibly cover every idea, character action, and character motivation--the world is too big and prose is too short. Thus, blanks are created in the text where readers have to use their own subjective experience to infer what happened in the blank space and complete the text. Reader response looks at how the audience helps create the text (reception theory) by examining how different individuals read different texts, how interpretation can be similar within a specific discourse community of readers with similar values, and how the emotional response of the reader creates significance in the text. Giants of this theory include Louis Rosenblatt, Staley Fish, and Wolfgang Iser.
CULTURAL POETICS is a discipline that seeks to discover how historical, political, cultural, anthropological, and economic context influences art and those who view art. the text through the view of the political context of either the author or reader. Essentially, authors construct a text within their historical experience, so we cannot ignore the social ideas and biases they had when they wrote a text. Likewise, a critic brings in their own biases and experience based on when they critique a piece, and followers of cultural poetics focus on how the critic's history influences how they perceive the text. Cultural poetics requires research, as a textual interpretation can only be justified in relation to other historical texts, whether they be other artistic works or primary source documents. Cultural poetics holds that all interpretations of a text are subjective and that a text holds no higher universal truth. There are three distinct schools of criticism within cultural poetics: authorial criticism (also called biographical criticism), New Historicism, and aestheticism.
Authorial criticism focuses on how the text is a reflection of its author: who the author was, what the author believed, the author's personal history, and the socioeconomic culture around the author at the time of the writing. By paring textual events and content (internal evidence) with research on the author's life by other scholars (intermediate evidence) and authorial commentary by the author on his or her own work (external evidence), the authorial scholar connects plot events in the story to events in the author's own life, pairs characters and their motivations in a text to actual people in the author's life, and reflects on the author's purpose for writing a text. The authorial critique also crosses with some psychoanalysis, as it often assumes an author's subconscious is also revealed in the text and that a close reading can reveal the id desires and repression of the author at the time of the writing.
While New Historicism also explores a work through its historical context, it ignores the author's intention and instead focuses on how the text reflects or goes against the popular ideology of its period. Spearheaded by the work of Michel Foucault and Stephen Greenblatt, New Historicists believe that sees all conflict as resulting from the conflict between conservatism (wanting life to remain constant to recent history) and progressivism (wanting life to appreciably change). This applies to both political history as well personal histories of characters (think Romeo and Juliet as progressives vs. their parents as conservatives). As this conflict drives history, New Historicists examine different discourses in a text and how they reflect the historical context around the text. This critique also examines the nature of language during the time and how popular fads influenced the construction and reception of the text, meaning that many New Historicists incorporate linguistics and literary movements.
Aestheticism is... strange. Aestheticism evaluates the beauty of a piece or art and how it adds value to the world. This critique was best summed up by Walter Pater: "It is art for its own sake." So how is beauty evaluated? According to Immanuel Kant, we must purge ourselves of our subjective desires in order to cultivate true taste. In “The Critic as Artist,” aesthete Oscar Wilde adds that criticism is above reason, sincerity, and fairness, and is subjective by design. Thus, each criticism of the beauty of a work becomes an independent and unique work of art itself. As a definition of analysis, this is... not helpful, which is why Terry Eagleton formalized an analysis of beauty as one that reveals a societal truth and causes a complete unexpected cathartic response. To keep the analysis in the realm of cultural poetics and out of reader response, modern aesthetes measure a text's beauty by its historical reaction, including its popularity and reception at the time of its release and the works that it inspired, as beautiful texts influence other texts. These influenced texts include both formal literary critiques and derivative intertextual works (like parodies and adaptations).
FORMALISM is the only category where the lenses are not reflective mirrors of another discipline or perspective-- rather, formalism focuses on the text alone in isolation from any other text or social context and dismisses any outside influences. Formalism is the most complex of all the lens groups, as it take a mature and practiced critic to divorce their analysis from their own contexts and biases. Formalism is essentially how a robot unconscious of history, politics, and emotion would analyze a text: with complete objectivity to meaning and content. Instead, formalism focuses on the mathematics of writing: grammar. Formalism examines the figurative language, diction, and syntax, and how each word and how its placed create meaning, regardless of what the sentence is actually saying. Formalists typically examine idiomatic language, sonance, meter (for verse), parallelism, and solecism, and formalism is very common in rhetorical analysis (though this doesn't extend to rhetorical appeals or fallacies--these are explored in societal, personal, and contextual critiques). Yet even an objective robot can have different focuses, thus there are three different formalist lenses: New Criticism, structuralism, and deconstruction.
Pioneered by Cleanth Brooks in The Well-Wrought Urn, New Criticism is the most popular formalist lens. New Criticism focuses on tension built in the text through the plot elements, specifically conflict, paradox (impossible contradictions possible only in artifice), ambiguity (words and phrases that are intentionally unclear and able to be interpreted differently), and irony. New Criticism is also famous for ignoring any authorial explanation or critique of their own text (as explained in Roland Barthes' essay "The Death of the Author"). This expands out to sequels, prequels, and other "official companions;" sorry, Harry Potter fans, but according to New Critics, Pottermore doesn't count. Other founding New Critical texts include “The Intentional Fallacy” (it doesn't matter what the author intended, only what is interpreted by the critic) and “The Affective Fallacy” (Aristotle was wrong--catharsis doesn't matter) by W.K. Wimsatt and Monroe Beardsley.
Also called semiotics, structuralism evaluates literature based purely on the elements of style. Based on the works of linguist Ferdinand de Saussure, structuralists believe that, since all language is based on patterns, looking at these patterns reveals deeper meaning, and that all words are essentially arbitrary signs to which the critic ascribes a meaning. Structuralism also, naturally, considers the overall structure of a text (myth, novel, play, etc) and how the choice in structure communicates meaning (though NOT if the structure is an effective way of communicating an author's intended meaning--that's aestheticism and reader response). Think poems: the whole idea that a sonnet's grammar makes it a different machine than a haiku is a structuralist notion. Note that this does not extend to genre tropes, as genre is defined by grouping texts together, and formalism is about texts in isolation (adherence to genre is, again, part of both reader response and aestheticism)
Related to structuralism is deconstruction, which is why it is frequently called post-structuralism. Deconstruction originates in Jacques Derrida's Of Grammatology and examines the dual elements in a text (e.g., “male vs. female,” “man vs. animal,” “speech vs. writing”) and examines the struggle for dominance between these binaries. While this could easily devolve into a societal mirror or cultural poetics, deconstruction observes the text in isolation and doesn't use terminology of agency--in the eyes of a deconstructionist, agency is isolated to the circumstances of a text and not a broader social context. For example, a deconstructionist would see the various couples in Pride and Prejudice (Darcy and Elizabeth, Jane and Bingley, Lydia and Wickham, etc) as binaries with independent antithetical qualities, while a feminist reader would see all these women as struggling together against dominant male agency.