By Speaking English, Modal verbs

There are advantages. The sentences above are probably what you want. "to can" is impossible. Modal verbs are defective verbs in that they have no infinitive forms. I didn't understand exactly what you wanted to say in the second part of your post. CJ

Let's first compare "would" to "could" in questions. "Could" means do you have the ability, whereas "would" means do you have the willingness: "Would you help me?" vs. "Could you help me?" We often use could to mean willingness as well, but it really should be "would." Now let's try some...