The question is based on an explanation from https://iep.utm.edu/kantview/ which states that what you should do, for Kant, is to "act rationally, in accordance with a universal moral law."
My understanding of Kant is this:
moral law = universal maxim+
maxim+ = what you are doing, and the reason why is because it is the right thing to do
maxim- = what you are doing, and the reason why is for some other reason not related to morals
What the right thing to do is = maxim+ that everyone can rationally follow and will to be = categorical imperative
What the wrong thing to do is = maxim+ that everyone cannot rationally follow and will to be
What you should do for some other reason = maxim- that gets you to the goal you want = hypothetical imperative
What you should not do for some other reason = maxim- that does not get you to the goal you want
Is this a correct understanding? Is it also true that actions that are morally relevant are the actions that have reasons based on the action considered in and of itself to be good or bad?
But my question would then be: Why does the fact that moral laws or universal maxims are pure truths of reason imply they are the right or moral thing to do? Or, if this is false, what is the justification for the claim that What the right thing to do is = maxim+ that everyone can rationally follow and will to be?
For example: consider the maxim "I will only sometimes lie, but tell the truth most of the time such that others can believe me in almost every circumstance."
I do not see why you could not will this become a universal truth which everyone acts on... But this seems to imply that lying is not bad in of itself; it is only bad if others assume I will lie to them as a result of the universalization. So I do not see the connection between universal truth of reason and the right thing to do. What is the connection Kant makes to justify the implication? Why does a universal maxim/categorical imperative = right thing to do?