Dictionary.com Word FAQs
What are the correct uses of could, should, and would?
Could (and 'might') suggest a possible outcome: She could change her mind. In most uses, should and would are interchangeable, but there are exceptions. If should is used with the meaning 'it could happen in the future', in the first person, then it is preferred for a sentence like "I would like to attend the event." Should appears with the first, second, or third person to express a sense of duty. Other than in first person, would is preferred for describing something that may happen in the future, such as "You really should thank them." Would appears with the first, second, or third person to express habitual practice, a hypothetical instance, or a preference. Many more American speakers use would than should (and will more than shall). Should is used in idiomatic expressions such as "I should think so!" The intended meaning guides the choice between these words. If you say, "I could eat a cow," this suggests that the potential is there for you to eat a cow. If you say, "I would eat a cow," this means that it is something that hypothetically you would do (especially if you are not a vegetarian). If you say, "I should eat a cow," then you are intimating that you may have a duty to eat a certain cow (or perhaps the leftover sloppy joes in the refrigerator).