Sometimes we use context to figure out with which meaning a word is being used, or which of several words that look or sound alike is being used, or even which language is being spoken. These are presemantic uses of context. I will contrast them with indexicals and anaphora, where context is used semantically.
Consider this utterance:
Knowing that this happened in Frankfort rather than San Francisco might help us determine that it was German teenagers expressing enthusiasm and not American teenagers expressing disgust. In this case context is relevant to figuring out which language (and hence which word with which meaning) is being used.
The vocable ``ich'' is a homonym across languages. Homonyms are words that are spelled and pronounced alike. For example, there are two words in English that are spelled and pronounced ``quail''; one is a noun that stands for a small game bird, the other a verb for faltering or recoiling in terror. It makes sense to speak of two words that are pronounced and spelled the same, because words are not merely patterns of sound or combinations of letters, but cultural objects with histories; our two words ``quail'' derived from different French and Latin words. The term ``vocable'' can be used for what the words have in common, so if we need to be precise we can say the vocable ``quail'' corresponds to two words in English.
Each of the German teen-agers, when they use the indexical ``ich,'' designates herself, and so the expression ``ich'' designates differently for each of them. One might be tempted to consider this just more homonymity. Each has a different name for himself or herself, they just happen to all be spelled alike and sound alike; we have homonyms across idiolects of the same language. Such a temptation should surely be resisted as an explanation of the shiftiness of indexicals. For one thing, the word ``ich'' doesn't have different historical origins depending on which teen-ager uses it; they all learned the standard first-person in German. The homonym account would be even worse for temporal and spatial indexicals. We would have to suppose that I use a different word ``tomorrow'' each day, since my use of ``tomorrow'' shifts its designation every night at the stroke of midnight.
An ambiguous expression like ``bank" may designate
one kind of thing when you say ``Where's a good bank?" while
worried about finances, another when I use it, thinking
about fishing.
Its
designation varies with different uses, because different of
its meanings are relevant. Again, all sorts of contextual
facts may be relevant to helping us determine this. Is the
speaker holding a wad of money or a fishing pole? It isn't
always simply the meaning of a particular word that is in
question, and sometimes questions of meaning, syntax and the
identity of the words go together:
With (2), knowing whether our speaker has just arrived from Germany or just arrived from Saudi Arabia might help us to decide what the syntactic structure of the sentence is and whether ``good'' was being used as an adjective or an adverb.
Is ``duck'' a noun or a verb in (3)? In this case, knowing a little about the situation that this utterance is describing will help us to decide whether the person in question had lost her pet or was seeking security in an earthquake.