Ought is a word that signifies responsibility for an action. This tentative definition implies that we will always know how that responsibility should be exercised. Immanuel Kant springs to mind. His thoughts on the matter should make matters clearer – after a little googling I came across this website http://philosophy.lander.edu/ethics/kant.html
Categorical imperatives are the key determining factor regarding what an individual ought to do, based purely on reason. Logical reasoning should guide us to a right action and that ethical imperative should be unconditional and universal.
No equivocation – no what if I have to kill to save a life dear to me? dilemma. Killing is always wrong, so we ought not to kill. Our moral duty could not be more clearly expressed.