Watson was created by IBM a long time before Siri's origin. Had IBM patented Watson (I am not sure if it did so or not), could it sue Apple for Siri on grounds that they copied their idea?
I am just trying to figure out the extent to which a patent can be used to defend one's <i>IP</i>.
Anybody can sue anybody for anything. The question is, do you have grounds to sue that won't get you laughed out of court.<p>Patents are supposed to cover implementations of inventions. Mere combination of existing ideas is not supposed to be covered. Watson and Siri (and Google Voice Search) combine voice recognition, natural language processing, and some sort of inference engine, but it's unlikely that any of them are using exactly the same techniques for all the parts.
Keep in mind it is much more complex than that. Siri comes from SRI International which did work for the Defense dept., etc. When Apple ate Siri Inc, which formed from SRI, they probably ate a lot of IP with it. SRI dates to like the 1950s at least.