Existentialism () is the work associated mainly with certain late-19th- and 20th-century European philosophers who, despite profound doctrinal differences, shared the belief that philosophical thinking begins with the human subject—not merely the thinking subject, but the acting, feeling, living human individual. While the predominant value of existentialist thought is commonly acknowledged to be freedom, its primary virtue is authenticity. In the view of the existentialist, the individual's starting point is characterized by what has been called "the existential attitude", or a sense of disorientation, confusion, or dread in the face of an apparently meaningless or absurd world. Many existentialists have also regarded traditional systematic or academic philosophies, in both style and content, as too abstract and remote from concrete human experience. 

Søren Kierkegaard is generally considered to have been the first existentialist philosopher, though he did not use the term existentialism. He proposed that each individual—not society or religion—is solely responsible for giving meaning to life and living it passionately and sincerely, or "authentically". Existentialism became popular in the years following World War II, and strongly influenced many disciplines besides philosophy, including theology, drama, art, literature, and psychology. 

The term is often seen as a historical convenience as it was first applied to many philosophers in hindsight, long after they had died. In fact, while existentialism is generally considered to have originated with Kierkegaard, the first prominent existentialist philosopher to adopt the term as a self-description was Jean-Paul Sartre. Sartre posits the idea that "what all existentialists have in common is the fundamental doctrine that existence precedes essence", as scholar Frederick Copleston explains. According to philosopher Steven Crowell, defining existentialism has been relatively difficult, and he argues that it is better understood as a general approach used to reject certain systematic philosophies rather than as a systematic philosophy itself. Sartre himself, in a lecture delivered in 1945, described existentialism as "the attempt to draw all the consequences from a position of consistent atheism".
Instead of what?
He proposed that each individual—not society or religion—is solely responsible for giving meaning to life