Dennett p 290
Consider a standard soft-drink vending machine, designed and built in the United States, and equipped with a transducer device for accepting and rejecting US quarters… Normally, when a quarter is inserted into a two-bitser, the two-bitser goes into a state, call it Q, which "means" (note the scare-quotes) "I perceive/accept a genuine US quarter now." Such two-bitsers are quite clever and sophisticated, but hardly foolproof. They do "make mistakes" (more scare-quotes). That is, unmetaphorically, sometimes they go into state Q when a slug or other foreign object is inserted in them, and sometimes they reject perfectly legal quarters - they fail to go into state Q when they are supposed to.
Dennett p 291
If objects of kind K [which also put the two-bitser into state Q] became more common in the two-bitser's normal environment, we could expect the owners and designers of two-bitsers to develop more advanced and sensitive transducers that would reliably discriminate between genuine US quarters and slugs of kind K. Of course trickier counterfeits might then make their appearance, requiring further advances in the detecting transducers, and at some point such escalation of engineering would reach diminishing returns, for there is no such thing as a foolproof mechanism. In the meantime, the engineers and users are wise to make do with standard, rudimentary two-bitsers, since it is not cost effective to protect oneself against negligible abuses.
The only thing that makes the device a quarter-detector rather than a slug-detector or a quarter-or-slug-detector is the shared intention of the device's designers, builders, owners, users. It is only in the environment or context of those users and their intentions that we can single out some of the occasions of state Q as "veridical" and others as "mistaken". It is only relative to that context of intentions that we can justify calling the device a two-bitser in the first place.
Dennett p 291 again
A particular two-bitser, straight from the American factory and with "Model A Two-bitser" stamped right on it, might be installed on a Panamanian soft-drink machine, hwere it proceeded to ear its keep as an accepter and rejecter of quarter-balboas, legal tender in Panama, and easily distinguished from US quarters by the design and writing stamped on them, but not by their weight, thickness, diameter, or material composition.
Such a two-bitser, whisked off to Panama (the poor man's Twin Earth), would still normally go into a certain physical state - the state with the physical features by which we used to identify state Q - whenever a US quarter or an object of kind K or a Panamanian quarter-balboa is inserted in it, but now a different set of such occasions count as the mistakes. In the new environment, US quarters count as slugs, as inducers of error, misperception, misrepresentation, just as much as objects of kind K do. After all, back in the United States a Panamanian quarter-balboa is a kind of slug.
Dennett draws a moral based on function:
The two-bitser was originally designed to be a detector of US quarters… No one would have bothered bringing it into existence had not this purpose occured to them. And given that this historical fact about its origin licenses a certain way of speaking, such a device may be primarily or originally characterized as a two-bitser, a thing whose function is to detect quarters, so that relative to that function we can identify both its veridical states and its errors.
And further:
I claim to apply precisely the same morals, the same pragmatic rules of interpretation, to the human case.
Dennett p 298; 300; 319
our own intentionality is exactly like that of the robot, for the science fiction tale I have told is not new; it is just a variation on Dawkins's (1976) vision of us (and all other biological species) as "survival machines" designed to prolong the futures of our selfish genes… not only have we no guaranteed privileged access to the deeper facts that fix the meanings of our thoughts, but there are no such deeper facts. Sometimes functional interpretation is obvious, but when it is not, when we go to read Mother Nature's mind, there is no text to be interpreted. When "the fact of the matter" about proper function is controversial - when more than one interpretation is well supported - there is no fact of the matter.
We cannot begin to make sense of functional attributions until we abandon the idea that there has to be one, determinate, right answer to the question: What is it for? And if there is no deeper fact that could settle that question, there can be no deeper fact to settle its twin: What does it mean?
Dennett p 311; 312
The Realism about intentional content that Burge assumes, along with Fodor and the others, is also presupposed by Putnam, whose Twin Earth thought experiments set the agenda for much recent work on these issues. We can see this clearly now, by contrasting our two-bitser with a Putnamian example. In the case of the two-bitser, the laws of nature do not suffice to single out what its internal state really means - except on pain of making misrepresentation impossible. Relative to one rival interpretation or another, various of its moves count as errors, various of its states count as misrepresentations, but beyond the resources of artifcat hermeneutics there are no deeper facts to settle disagreements.
Consider then the members of a Putnamian tribe who have a word, "glug", let us say, for the invisible, explosive gas they encounter in their marshes now and then. When we confront them with some acetylene, and they call it glug, are they making a mistake or not? All the gaseous hydrocarbon they have ever heretofore encountered, we can suppose, was methane, but they are unsophisticated about chemistry, so there is no ground to be discovered in their past behavior or current dispositions that would license a description of their glug-state as methane-detection rather than the more inclusive gaseous-hydrocarbon-detection. Presumably, gaseous hydrocarbon is a "natural kind" and so are its subspecies, acetylene, methane, propane, and their cousins. So the laws of nature will not suffice to favor one reading over the other. Is there a deeper fact of the matter, however, about what they really mean by "glug"? Of course once we educate them, they will have to come to mean one thing or the other by "glug", but in advance of these rather sweeping changes in their cognitive states, will there already be a fact about whether they believe the proposition that there is methane present or the proposition that there is gaseous hydrocarbon present when they express themselves by saying "Glug!"?