Reasoning from first principles is the process of breaking a problem down into the fundamental parts that are known to be true, and then building up a solution from there. It can apply to effectively learning new topics, as well as generating new solutions to problems, or redefining a problem so an existing solution can be employed. Make no assumptions.
References
Link to originalElon Musk
“I do think there is a good framework for thinking. It is physics–you know the sort of first principles reasoning. … What I mean by that is boil things down to their fundamental truths and reason up from there as opposed to reasoning by analogy.
Though most of our life, we get through life by reasoning by analogy, which essentially means kind of copying what other people do with slight variations. And you have to do that, otherwise, mentally, you wouldn’t be able to get through the day. But when you want to do something new you have to apply the physics approach. Physics has really figured out how to discover new things that are counter-intuitive, like quantum mechanics … so I think that’s an important thing to do. And then also, to really pay attention to negative feedback and solicit it, particularly from friends. This may sound like simple advice, but hardly anyone does that and it’s incredibly helpful.”
Source: TED talk - Elon Musk: Revolutionizing the Energy Industry