Is intention the result of rational or logical thinking or some other?

According to one of many sources, the definition of intention is described as Right intention is the intention and resolve to give up the causes of suffering, to give up ill-will and to adopt harmlessness. It contrasts with wrong intention, which involves craving for worldly things (wealth, sex, power) and the wish to harm. What is unclear is whether intention is an act or thought that precedes or follows rational thought? My understanding is that intention plays a critical role in one karma. If my thought is the result of anger however i do not have intent to harm is that not the result of rational thought? If i do act irrationally, to save or protect a life, is that not intention without thought? **EDIT** To add to ChrisW's question on clarification, when i say that if my thought is of anger e.g. how this person would disappear or no longer be around, but this is not followed by action because rationally i do not wish to cause harm. The second example of irrational thought is that when caught in the spur of the moment, i may say or do things however this is to protect a child.