Acting out of duty

According to one reading of Kant,

1. If A is an obligatory action, one maximizes the praiseworthiness of the action when one does A solely out of duty.[note 1]

But (1) is false. (Whether Kant actually held to (1) is irrelevant.)

To see that (1) is false, note that it is better to do a supererogatory action because it goes over and beyond duty than it is to do an obligatory action because it is in accord with duty. Now suppose I do something good for my friend solely out of duty. If I am acting solely out of duty, then the following counterfactually will typically be true:

2. If A were not (or maybe: not seen as) a duty, then one would not have done it.

But a dutiful action that benefits a friend and that satisfies (2) is less good than an action that satisfies:

3. If A were not a duty, then one would still have done it on account of its then being supererogatory.

A set of reasons for action that makes (3) true is morally superior to a set of reasons that makes (2) true. But a set of reasons making (3) true will be distinct from A's simply being a duty. Consider the following reasons one might have for doing A:

4. A's being either a duty or supererogatory.
5. A's being a benefit to one's friend and not a violation of any duty. out of sole motive of duty.

I submit that if A is overdetermined by the reason

6. A's being a duty

together with either (4) or (5) (so that (6) is a sufficient motive and so is (4) or (5)), it is morally superior to an action that proceeds solely from (6). This is because such an overdetermined action is both respectful of duty and exhibits the laudatory counterfactual (3). This is better than acting solely from duty, since that would falsify (3).