Base, low, vile mean contemptible because beneath what is expected of the average man.
What is base excites indignation because devoid of all nobility or even of humanity; the term usually implies the setting (as through cowardice or avarice) of self-interest ahead of duty to others.
What is low outrages one's sense of decency or propriety. The term, when implying moral contemptibility, often suggests a taking advantage (as by cunning, deceit, or other devious practice) of a person who is helpless or not in a position to defend himself.
Low also is often used of persons, thoughts, language, or actions that strongly offend one's sense of propriety.
What is vile is inexpressibly base or low; the word often implies disgusting foulness or depravity.