In cognitive science and semantics, the symbol grounding problem concerns how it is that words (symbols in general) get their meanings, and hence is closely related to the problem of what meaning itself really is. The problem of meaning is in turn related to the problem of how it is that mental states are meaningful, hence to the problem of consciousness: what is the connection between certain physical systems and the contents of subjective experiences. Background Referents Gottlob Frege distinguished a referent (the thing that a word refers to) and the word's meaning. This is most clearly illustrated using the proper names of concrete individuals, but it is also true of names of kinds of things and of abstract properties: (1) "Tony Blair", (2) "the prime minister of the UK during the year 2004", and (3) "Cherie Blair's husband" all have the same referent, but not the same meaning. Some have suggested that the meaning of a (referring) word is the rule or features that one must use in order to successfully pick out its referent. In that respect, (2) and (3) come closer to wearing their meanings on their sleeves, because they are explicitly stating a rule for picking out their referents: "Find whoever was prime minister of the UK during the year 2004", or "find whoever is Cherie's current husband". But that does not settle the matter, because there's still the problem of the meaning of the components of that rule ("prime minister", "UK", "during", "current", "Cherie", "husband"), and how to pick them out. The phrase "Tony Blair" (or better still, just "Tony") does not have this recursive component problem, because it points straight to its referent, but how? If the meaning is the rule for picking out the referent, what is that rule, when we come down to non-decomposable components like proper names of individuals (or names of kinds, as in "an unmarried man" is a "bachelor")? Referential process Humans are able to pick out the intended referents of words, such as "Tony Blair" or "bachelor," but this process need not be explicit. It is probably an unreasonable expectation to know the explicit rule for picking out the intended referents. So if we take a word's meaning to be the means of picking out its referent, then meanings are in our brains. That is meaning in the narrow sense. If we use "meaning" in a wider sense,