From Clay Shirky’s “The Semantic Web, Syllogism, and Worldview“:
What is the Semantic Web good for?
The simple answer is this: The Semantic Web is a machine for creating syllogisms. A syllogism is a form of logic, first described by Aristotle, where “…certain things being stated, something other than what is stated follows of necessity from their being so.” [Organon]
The canonical syllogism is:
Humans are mortal
Greeks are human
Therefore, Greeks are mortal
with the third statement derived from the previous two.
The Semantic Web is made up of assertions, e.g. “The creator of shirky.com is Clay Shirky.” Given the two statements
– Clay Shirky is the creator of shirky.com
– The creator of shirky.com lives in Brooklyn
you can conclude that I live in Brooklyn, something you couldn’t know from either statement on its own. From there, other expressions that include Clay Shirky, shirky.com, or Brooklyn can be further coupled.
The Semantic Web specifies ways of exposing these kinds of assertions on the Web, so that third parties can combine them to discover things that are true but not specified directly. This is the promise of the Semantic Web — it will improve all the areas of your life where you currently use syllogisms.
Which is to say, almost nowhere. …
Despite their appealing simplicity, syllogisms don’t work well in the real world, because most of the data we use is not amenable to such effortless recombination. As a result, the Semantic Web will not be very useful either. …
In the real world, we are usually operating with partial, inconclusive or context-sensitive information. When we have to make a decision based on this information, we guess, extrapolate, intuit, we do what we did last time, we do what we think our friends would do or what Jesus or Joan Jett would have done, we do all of those things and more, but we almost never use actual deductive logic. …
Syllogisms sound stilted in part because they traffic in absurd absolutes. …
There is a list of technologies that are actually political philosophy masquerading as code, a list that includes Xanadu, Freenet, and now the Semantic Web. The Semantic Web’s philosophical argument — the world should make more sense than it does — is hard to argue with. The Semantic Web, with its neat ontologies and its syllogistic logic, is a nice vision. However, like many visions that project future benefits but ignore present costs, it requires too much coordination and too much energy to effect in the real world, where deductive logic is less effective and shared worldview is harder to create than we often want to admit.