An assumption is something taken for granted. Everyone makes assumptions--you have to in order to say anything. As a critical reader, you need to determine what the assumption is and then decide whether you agree or disagree with the assumption. Once you decide, your attitude toward the argument will change. Careful, honest writers know what their assumptions are and lay the most important ones out for all to judge. Hidden assumptions may be all right for humor or fairly harmless in topical journalism, but they can be dangerous in serious written argument. Important assumptions should be explicit and detailed, for then the reader can judge their validity. If you do not agree with a writer's assumptions, then you will never agree with his/her arguments.
As indicated above, an assumption is a belief that we take for granted as a basis for an assertion. All kinds of statements rely on assumptions--questions, commands, promises, and assertions. The simple command "Pass the salt" is based on several assumptions, including that the salt can be passed, that you can pass it, and that I have the right to ask you to pass it. Some assumptions are unexpressed. We would be the joke of the neighbourhood if we went around articulating our assumptions every time we asked someone to pass the salt. We get into trouble, however, when we fail to recognize important assumptions that subtly guide our thoughts. Sophocles said, "Reason is God's crowning gift to man. "A statement like this seems innocent enough. When we think about it, we easily recognize that he was basing the statement on two major assumptions: (1) that man has a mind, and (2) that God exists. Hidden in the statement, however, are some subtle assumptions that we may or may not support, including: (1) God is a personal force capable of making a gift; (2) reason is a more important gift than heart, soul, or body; and (3) woman's mind is not a gift of God. Once we articulate these assumptions, we might disagree.
According to this passage, an assumption is ______.

A. something that everyone knows
B. the idea the writer wants to emphasize
C. the reader's knowledge about the topic
D. foundation of the writer's reasoning