The base of an object is its lowest part, where it begins, or where it touches the ground or a surface.

1. We reached the base of the volcano.
2. …a small hole at the base of the cylinder.

A base for a system of ideas or a subject of study is the foundation from which other ideas or more advanced studies are developed.

3. …the compulsory base on which post-school education rests.
4. Society is natural and has a spiritual base.
5. Marx came to describe the economy as a base, or structure, upon which a superstructure was erected consisting of such elements as law, politics, philosophy, etc.

The basis of or for something is the central and most important part of it, from which it has been or can be further developed.

6. The court is quite satisfied that there is no basis for these criticisms.
7. This figure has been adopted as the basis for the Government’s longer-term planning in higher education.
8. This was the basis of the final design.