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Giles Corey is a strong old man who has only recently converted to Christianity. He's likable, but is not too bright. His biggest bumble in the play is when brings up the fact that his wife reads strange books. To Giles, any book is strange and the idea of a woman wanting to read totally blows his mind. His mention of this fact leads to an accusation that his wife is a witch.
Giles feels terrible about this. He knows his wife is innocent and recognizes that his own actions have led to her incarceration and impending death. He attempts to defend his wife by going to the court and showing them proof that, in at least one case, the accusation is based on Thomas Putnam’s greed for a neighbor’s bit of land. This backfires and he is condemned himself.
Corey's incredible strength of character is shown in the end when he neither confesses to, nor denies, the charges of witchcraft. By doing so, he ensures that his sons can legally inherit his property. Even though he is brutally tortured by having crushingly heavy stones place on his chest, the only thing Giles says is "More weight" (IV.186).
Miller would go on to pull a "Giles Corey" of his own when he was called to testify before McCarthy's Un-American Activities Committee. Despite tremendous pressure, Miller refused to name names of suspected Communists.