We can divide sentences which require context into those which contain indexicals, and which therefore require a perceptual context, and those which require a linguistic context (or those which require both, but this is not an important or separate case). An indexical is a term which requires a perceptual background in order to be intelligible. The background will determine which object is pointed to, or which place is 'here' or which time or date is 'now', and so on. The context requirement for indexicals is therefore limited.
The requirement for linguistic context must also be limited, for if the context-supplying language A itself required a linguistic context B, and if B required yet another context C, there would be an infinite regress, and nothing would be intelligible. But language is intelligible, therefore the requirement for linguistic context must be limited.
As an example of the limitation of linguistic context, consider:
A man and a boy were standing by a fountain. The man had a drink.The sentence 'the man had a drink' requires a context in order for its meaning to be properly understood, for the description 'the man' tells us which of the two individuals standing by the fountain had a drink. The context is supplied by the preceding sentence 'A man and a boy were standing by a fountain', which requires no further context. We understand the first sentence simply by understanding the meanings of 'a', 'man', 'and', 'boy' and so on, and this understanding should be available to any competent speaker of the language. As a result, the two sentences together require no further context at all. Any competent user of the language can understand them, as long as they are available together, and as long as their correct sequence is determined by the physical nature of the text (or by some other method of determinate ordering).