 “and” and “but” contribute the same way to truth and falsity. However, when using  (9b),  but not when using  (9a),  the speaker indicates that there is a contrast of some kind between working with real estate and liking fishing. The speaker is not asserting that there is a contrast. We can test this, for instance, by forming a conditional with  (9b).  The antecedent of (10) preserves the contrast rather than make it hypothetical, showing that the contrast is not asserted, forming a conditional with  (9b)  in the antecedent preserves the contrast rather than make it hypothetical: