Developed in the ninth and tenth centuries in Western Europe, Gregorian chants are a simple, monophonic form of music used as sacred music by monks in the Catholic tradition. Gregorian chants helped spread the Latin Rite of Roman Christianity by having a common, uniform musical style for worship. Among certain monastic orders, the Gregorian chant is still a common form of worship.

In a way, all of these thinkers were influential, though in different ways. Francisco de Vitoria was a teacher in Spain whose work on natural rights is part of a broader discussion that would eventually filter through many Catholic and Protestant thinkers. These thinkers would become sources for the pivotally important Thomas Hobbes, whose best known political work is the _Leviathan—_a brutal but fully developed treatise on a quite domineering notion of the nation state. Likewise, Baron de Montesquieu was quite influential on many political thinkers during this period, as was Jean-Jacques Rousseau.

The most important thinker concerning the Declaration of Independence is John Locke. It is from Locke's thought that Thomas Jefferson derived his remarks regarding the rights to "life, liberty, and the pursuit of happiness." In Locke's political philosophy, he actually presents life, liberty, and property as the three fundamental rights of human persons. Locke's position was a kind of softening of the much harsher position of Hobbes, who stated that when we are not in society, we only have one fundamental right—self defense! Note, of course, that Jefferson changed "property" to "pursuit of happiness." This followed the recommendations of his fellow drafters, who hoped thereby to avoid issues that could have arisen because of a very problematic form of property in the colonies—slaves.

H.P. Lovecraft was a writer who toiled away in his own life in relative obscurity, writing horror and science fiction pieces for small magazines. After his death in 1937, however, Lovecraft's stories, which featured otherworldly scenarios, horrible creatures, and threats to humanity, gained a larger popularity. In modern times, Lovecraft is seen as one of the foremost science fiction and horror authors.

Gregorian chant is the style of music that developed throughout the Middle Ages, having various sources and styles. It was an ecclesiastical form of music, meaning that it was a "church" music. In particular, it was a kind of liturgical music, used in the various forms of public worship undertaken by the Latin Roman Catholic Church. Its melodies were based on the texts of the Mass, the Divine Office, and other liturgical ceremonies. Many of these texts were biblical, though adaptations from other sources are also found in many hymns and antiphons throughout the Middle Ages.

The Brothers Karamazov took Fyodor Dostoevsky over two years to write, and he intended the massive work as the first in a series, but he died four months after its publication. The novel concerns the Karamazov family, led by patriarch Fyodor Karamazov and his three sons of young adult age, the hotheaded Dmitri, the rational Ivan, and the faithful Alexei. Philosophical and emotional conflicts drive the plot and themes of the lengthy novel.

A Streetcar Named Desire won the 1948 Pulitzer Prize in Drama for its playwright, Tennessee Williams. Largely considered one of the premier dramas of the twentieth century, the play's depiction of mental health problems, sexual desire, and violence was considered groundbreaking in its own time. The play would be made into an award-winning movie in 1951 and firmly established Tennessee Williams as one of the largest figures of the theater world.

Arthur Miller won the Pulitzer Prize in Drama in 1949, David Mamet won the Pulitzer Prize in Drama in 1984, Eugene O'Neil won the Pulitzer Prize in Drama in 1922, 1928, and 1957, and Sarah Ruhl won the Pulitzer Prize in Drama in 2010.

The philosophy of Plato is known for many things. One of his most famous doctrines is the so-called theory of "Forms" or "Ideas." This refers to the notion that everything in the world "participates" in some kind of universal and separate Idea. Thus, we can only call this or that tree a "tree" because those various individual trees participate in the universal notion of "treeness."

This position is often called "extreme realism" because it supposes that our ideas are so real that they actually exist. It is like there is a kind of "heaven" (loosely speaking) in which the Ideas exist. A radically contrary position is sometimes named "nominalism", which indicates that there are no universal Ideas that are really "out in reality." Instead, a strictly "nominalist" position would state that universal ideas like "tree" and "dog" only exist because we give name to individual things.

The 1895 novel, The Red Badge of Courage, was Stephen Crane's second novel, but his first success, making him a literary celebrity at the age of 24. Crane was inspired to write a tale of the Civil War thirty years after the end of the conflict, after reading tales of battles from veterans. Crane thought the journalistic reports did not convey what it was like psychologically to be in war, and so he crafted his story about a soldier by interviewing a host of Civil War veterans about their experiences.

Aristotle was a Greek scientist and philosopher. Sophocles is most famous for his three Theban plays. Aeschylus wrote The Oresteia trilogy. Aristophanes wrote comedies and Euripedes wrote dramas in Athens.

Modernism was a movement that spread through many different forms of art in the last decade of the nineteenth century. Modernism rejected what the artists saw as outdated modes. In poetry, the movement was summed up by Ezra Pound's advice to "Make it new!" and Wallace Stevens' use of blank verse, along with T. S. Eliot's writing lengthy epics of mundane life, and E.E. Cummings' reshaping the physical look of poetry. Many modernists were intentionally rejecting the romantic poets like William Wordsworth.