心智的活动，除了尽力产生各种简单的认识之外，主要表现在如下三个方面：1）将若干简单认识组合为一个复合认识，由此产生出各种复杂的认识。2）将两个认识放在一起对照，不管它们如何简单或者复杂，在这样做时并不将它们合而为一。由此得到有关它们的相互关系的认识。3）将有关认识与那些在实际中和它们同在的所有其他认识隔离开，这就是抽象，所有具有普遍性的认识都是这样得到的。
John Locke, An Essay Concerning Human Understanding
（有关人类理解的随笔，1690）



The acts of the mind, wherein it exerts its power over simple ideas, are chiefly these three: 1. Combining several simple ideas into one compound one, and thus all complex ideas are made. 2. The second is bringing two ideas, whether simple or complex, together, and setting them by one another so as to take a view of them at once, without uniting them into one, by which it gets all its ideas of relations. 3. The third is separating them from all other ideas that accompany them in their real existence: this is called abstraction, and thus all its general ideas are made.
John Locke, An Essay Concerning Human Understanding
(1690)