Reaching a conclusion before formulating an argument

What is a good word for saying that a person has reached a conclusion before properly formulating an argument?

For example, a logical train of thought would be 'My current computer is slow, this is decreasing my productivity, so therefore I would solve this by buying a new computer', whereas a person using this type of reasoning would say 'I want a new computer, let's think up reasons why this would be good. I know, I think I'm not working as well as I possibly could be.'

Solution 1:

You could be said to be rationalizing your behavior or your decision.

One definition of rationalize is:

To devise self-satisfying but incorrect reasons for one's behavior.