At this IBM research site, an interesting way to assess the themes in presidential inaugural addresses. The researcher, Jonathan Feinberg, uses fancy math to analyze which words in an address are most similar to those other presidents have used -- and which are most distinctive. The larger the words in the diagram, the more often a President used them in a given speech -- and the bluer they are, the more unusual their use is, compared with other speeches. The pink words are ones "conspicuously absent" from a speech -- ones showing up in other inaugural speeches but not this one.
For instance, this is the graph of GW Bush's Wilsonian-sounding Second Inaugural Address, with its commitment to "the expansion of freedom in all the world." Blue words are those distinctive to this speech; pink ones, those strikingly missing.
Disappointingly, the tool is not yet sufficiently honed to track the Reagan-era-onward emergence of "God bless America!" as the unvarying conclusion of presidential speeches. (In fairness, Obama left it out of the prepared text of his address this year.) And it's not set up to let you feed new rhetoric into it for analysis -- for instance, the tantalizing possibility of sluicing in newspaper columns, to depict the phrases a writer stresses and avoids. That's why researchers must still toil on. Thanks to Henry Farrell.