汉语与英语的可数性是无法对应的，所以要仔细品味英文释义。靠中文“基础”来理解foundation当然不靠谱

查牛津

[countable, uncountable] foundation

a principle, an idea or a fact that something is based on and that it grows from

例句：Respect and friendship provide a solid foundation for marriage.

由此例句，我们完全可以推导出以下例句

There are five solid foundations for marriage, among which mutual understanding is the most important.