There were few liberals and just one woman on the federal appeals court in Chicago when Diane P. Wood, an antitrust expert with a flair for foreign language and an ear for playing the oboe, showed up in the summer of 1995. The chief judge, a scholarly conservative named Richard A. Posner, promptly gave her some advice.

The appeals bench, Judge Posner warned, was like “a system of arranged marriage with no divorce.” His message to his junior colleague was clear: Pick your battles carefully. Compromise when you can.

In the 15 years since, Judge Wood, 59, has done just that, playing the role of philosophical outlier, a left-leaning woman in a world of right-leaning men, including Judge Posner and Judge Frank H. Easterbrook, a sharp-tongued intellectual who is now the court’s chief. The three have a long history together; all are former law professors at the University of Chicago, where an ambitious young state senator named Barack Obama made a name for himself lecturing on constitutional jurisprudence.

Now President Obama is considering Judge Wood as a possible Supreme Court nominee. With conservatives attacking her as too liberal, her long relationship with Judges Posner and Easterbrook — sometimes yielding surprising consensus, at other times spirited dissent — offers hints into just what kind of justice she might be.

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