underpinning
/ˈʌndəˌpɪnɪŋ/noun
1- a solid foundation laid below ground level to support or strengthen a building基础; 支承结构。
1.1
- a set of ideas, motives, or devices which justify or form the basis for something（理论、动机、学说的）基础：
the theoretical underpinning for free-market economics.
自由市场经济的理论基础。