For the other sciences it´s easy to point to the most important equations, inequalities, propositions or concepts that ground the discipline. If I want to explain Finance to a physicist say, **what are considered to be the most important equations, inequalities, propositions or concepts that underly the subject which I should introduce and attempt to explain**?

Above paraphrased from: http://economics.stackexchange.com/questions/35/what-are-the-foundational-equations-of-economics

My guess would be the [fundamental theorem of asset pricing][1] or some [Pricing Principle][2], but that's coming from a mathematical finance background. Would people coming from a corporate or personal finance (or [whatever else finance][3] is out there) background say something similar?


  [1]: https://en.wikipedia.org/wiki/Fundamental_theorem_of_asset_pricing
  [2]: https://quant.stackexchange.com/questions/14064/pricing-principle-1
  [3]: https://en.wikipedia.org/wiki/Finance#Areas_of_finance