Betsy newmark of "Betsy's Page" writes about Supreme Court Justices and their tendency to migrate to the left, and also gives an excellent definition to the way liberal and conservative labels apply to judicial philosophy:

I was talking with a friend the other day about this perceived tendency for justices to become more liberal. While there are some very prominent examples, I held that the sample size was not large enough to draw conclusions. I'm using liberal and conservative here as labels for their judicial philosophy not their partisan ideology. I would term anyone who thinks that we have a "living Constitution" as liberal and one who doesn't think so as conservative. Feel free to mentally substitute whichever term you prefer.

Look at the current Court to see if this theory about justices drifting to the left holds up. I don't count Souter and Stevens, although they were nominated by GOP presidents. They were pretty liberal all along. Ginsburg has always been liberal. Breyer is generally liberal, but he has voted on the side that could be labeled conservative a few times and I'm sure disappointed liberals when he did so. O'Connor and Kennedy have drifted to what seems to be the liberal side more frequently on some key votes but have gone back and forth. However, Rehnquist, Scalia, and Thomas have been reliable conservative votes. So, from that small sample, I don't know that we can generalize that conservative justices will become liberal. Some will, but some will remain firm in their original convictions. The real problems (in my view) are with the ones who were liberal to begin with and got appointed by presidents who either wanted a moderate like Ford choosing Stevens or were deceived about their nominee's views like Bush and Souter.

So those who fear "another Souter" don't have that much to worry about if the nominee, as Roberts seems to be, has a long history of firm conservative beliefs. Most importantly, he has a deep belief in the limited role of judges. That, more than a stand on any single issue, is what I was looking for in Bush's nominee. And so far, everything that has come out about Roberts goes to show that conservatives have a very good nominee in John Roberts.
http://betsyspage.blogspot.com/