In Ray Bradbury's novel, Fahrenheit 451, Clarisse McClellan is especially significant for several reasons.
First, Clarisse makes us look more closely at Guy in that she is very different. Montag is a man that does what is expected of him. He rarely asks questions or looks beneath the surface of life. He burns down houses with books inside and, at the beginning, does not see this as a bad thing.
Clarisse changes Montag, but not intentionally. One source describes her as "innocent." Her take on life is extraordinary as Montag sees it, and slowly her attitudes take root in Montag's heart and soul. Bradbury describes Clarisse:
Her face was slender and milk-white, and in it was a kind of gentle hunger that touched over everything with tireless curiosity. Her dress was white...
The repeated references to "white" (symbolic of purity) support the presence of innocence in Clarisse. She is learning about the world herself, as Montag eventually will also do; this is evident in her ardent curiosity.
Clarrise is not at all worried about doing what society and/or the government expects. She is a free-thinker who sees the world in terms of possibilities and simple pleasures in life that most people have forgotten, like "dew on the grass in the morning" and "a man in the moon." She tastes the rain and places a dandelion under her chin, and they his, to see if each is "in love." What really makes Montag start to think is Clarisse's odd question—to Montag's way of thinking—when she asks:
Are you happy?
In comparing Clarisse and Montag, we see two extremes of those who live in this society. We also learn that Clarisse represents a minorty—of the curious, the question-askers. Montag represents all that is wrong with society in this futuristic environment, questioning nothing...at first.
Clarisse is the one that simplifies life for Montag: she notices the passing landscape. She and her family members visit and talk, and do not feel controlled or compelled to conform. It is only after meeting Clarisse and speaking with her several times that Montag begins to more openly wonder about things, and to question society-driven norms.
Clarisse is symbolic of "dangerous" behavior. She is symbolic, too, of change: for within her character, Montag starts also to question, look beneath the surface and see things as they are rather than as he has been instructed to see them. Clarisse is the impetuous that allows Montag to ultimately break free of society's dictates—even to kill Beatty—and join others who wish to preserve the knowledge kept in books...even while society destroys itself.
Clarisse is also a foil to Mildred—Montag's wife. A foil is a...
...character who sets off another character by contrast.
Mildred is at the center of Montag's life. She does what society tells her to—without question—even if it is not good for her. Through Mildred we see Montag drifting away from what the world expects: he cannot rationalize Mildred's zombie-like behavior and her desire to separate herself from the real world.
Clarisse, on the other hand, does all she can to grab life with both hands.
Eventually, Clarisse's family disappears and she is said to have been killed in a car accident. I have wondered if this is true or if society simply "removed" Clarisse and her family because they would not conform. However, by the time this happens, Montag has been changed forever by Clarisse.