In a comment on the More on Supposedly "Clear" Texts thread, commenter von writes (in response to my text, which he italicized):

More on Supposedly "Clear" Texts: In the post below, I made a simple claim: You can't tell whether a text is "clear" or "unambiguous" by simply consulting the text — you also need to see whether there is external evidence that the meaning of some term is something other than what you assume it to "clearly" or "unambiguously" be (whether we refer to the meaning intended by the author or the meaning likely understood by most of the author's intended readers). This shouldn't be politically or ideologically controversial. It's just a description of how language and communication works.

A bit off point, but it's worth noting that the process used to construe a patent's claims (the part of the patent that tells you the scope of the patentee's zone of exclusion) *generally* proceeds in the opposite direction: A court looks first to instrinsic evidence -- roughly, the four corners of the patent document + the back and forth with the patent office during the application process -- to construe a claim or claim term. Only if the claim or claim term remains ambiguous does the Court typically consider so-called "extrinsic evidence," e.g., expert testimony, dictionary definitions, and the like.

I say "generally" because different panels of the Federal Circuit have, at times, expressed different views on when and how extrinsic evidence should be considered. The most recent in banc decision on the subject suggests a slightly preferred view of some extrinsic evidence (expert testimony), but doesn't quite elevate it to the level of intrinsic evidence in the claim construction process.

I'm no patent maven, but I wonder whether this can really be so. The commenter lists "dictionary definitions" as "extrinsic evidence" that can only be checked when the "intrinsic evidence" yields ambiguity. But surely the judges construing the patent claims are using their own mental dictionary to determine what the intrinsic evidence means in the first instance. Yet all of our mental dictionaries are incomplete, especially as to technical areas in which we aren't specialists. How could it make sense for a judge to rely entirely on his likely flawed mental dictionary, coupled with what's in the claim and in the back-and-forth with the patent office, and to simply refuse to consult a written dictionary if the possibly flawed mental dictionary gives a supposedly "unambiguous" answer?

Say a judge, using his own mental dictionary, thinks some term is unambiguous, because he's aware of only one definition -- perhaps partly because he's not a specialist in the relevant technical field, and thus doesn't know the field's technical definitions. A litigant comes and says "No, wait, look at this dictionary [either a general dictionary or a scientific dictionary], which lists this other definition, which is the definition that I and the patent examiners used, though we didn't mention it in the patent because we took it for granted."

Would a judge really say, "nope, I may not be a specialist in computers, but I think the term 'dump' unambiguously means 'throw out' [which is to say, it unambigously means 'throw out' in my own mental dictionary], so I'm going to refuse to consider a computer science dictionary, even though you claim it gives an alternate definition"? If so, how is this remotely sensible?