The propositional content of a sentence gets a contextual meaning when it is judged in a given situation or context. This might be a reason, justification, assumption, explanation, or other functions that the sentence might assume from the context. The functional value of a sentence is derived from the writer's intention in using it, and it is identified from the relationship between this sentence and others in the same text. For example, when it stands alone, the proposition I like the thinking process that goes with it just gives the view of the speaker. But when it follows the sentence I'd take several courses in philosophy (Returning to College: Para. 6), it assumes the function of giving a reason or justification. The writer uses it to explain why he would take philosophy courses. Sometimes, the writer uses signal words to indicate the functional value or contextual meaning. For instance, but, however or nevertheless are often used to signal a change of thought, and because, since, or therefore to signal an explanation or reasoning.