American legal realism is kind of hard to pin down to any few core tenants. In some ways, maybe it's more of a disposition or an attitude than it is a set of principles. I guess one way to talk about it is what it's not. The phrase realism is an alternative to formalism. The realist narrative: American lawyers in the late 19th century assumed that a careful lawyer could study a series of sources and figure out what they said no matter where you started. And that law could be studied by looking at sources without consulting anything outside those sources, and that every source ended up leading to a rule. Realists thought that law was not only formed; there was some realistic assessment of choices that needed to be made by policy makers. I'd say American legal realists shared a lot of the same interests and a lot of the same motivations as Bentham had. The American legal realist assumed that the way the economy in the US and politics were changing in the early 20th century; there a lot of laws needed to change to catch up with the changes that were happening in the economy and in the country. And they thought that the law as it had been seen by the formalists was too brittle, and it was not up to the job of keeping up to the times. Realists tended to suspect that there's a lot of judgment that needs to be exercised by the lawyer, and it was more often the case that if there was one source, three lawyers would see the source three different ways. Three different lawyers would then rely on background judgments and opinions about good policy to infuse how they looked at the law. And those applied judgements would then lead them to see the same source in different directions. Most academics and sophisticated lawyers would say: yeah, we're all realist now. But then if you ask them all, what does realism require in a particular set of issues, this is the kind of topic where you're going to get different opinions from different people. I'd say a realist approach starts with what legal sources say, and then says: what do these sources require and what discretion do they leave open? And a realist is prepared to believe that a source closes a few doors and leaves many, many more doors open. A realist then thinks that to choose which of those doors to go through, to choose how to take an underdetermined legal source and give it more determinacy; one needs to identify all the relevant policies that come to bear on the practical problem, and then figure out what good policy requires within the limits of what the law allows. A realist wants to make a prescription about what the law requires, making a judgment that's particular to one set of circumstances. Realists like to think that legal rules ought to be made one case at a time. Legal realists tend to resist the idea that you can make a statute, or you can make a common law rule that settles broad classes of cases with very, very few exceptions.