这两个术语均有策划、鼓励、协助或唆使他人犯重罪，即具有“从犯”（accessory)的含义。

按传统，“从犯”曾包括accessory before the fact (事前从犯）和 accessory after the fact (事后从犯）两类。

accessory before the fact 和 principal (主犯）的区别在于前者未出现而后者则出现在犯罪现场，有时缩写为「accessory before」。目前美国多数州的法规已经废除此种区分而将accessory before the fact当作共犯归类为principal。A person who aids, abets, or encourages another to commit a crime but who is not present at the scene. An accessory before the fact, like an accomplice, may be held criminally liable to the same extent as the principal。

accessory after the fact则是指明知犯罪已经实施，帮助犯罪人逃脱逮捕或惩罚者。在美国，根据大多数州刑事法律的规定，对于事后从犯作单独处理，有4条要求：１他人已经实施了重罪，而且必须在从犯实施之前已经完成；２从犯不能与主犯同罪；３从犯必须亲自帮助主犯以避免重罪处罚；４从犯的帮助必须具有明知故意。《模范刑法典》〔Model Penal Code〕认为事后从犯其实不是共同犯罪人，按「妨碍审判罪」另行处理。有时缩写为「accessory after」。现多数州已不再笼统使用此术语，而将其分为若干具体的犯罪，如干扰司法罪“obstructing justice” 等。An accessory-after-the-fact is someone who assists 1) someone who has committed a crime, 2) after the person has committed the crime, 3) with knowledge that the person committed the crime, and 4) with the intent to help the person avoid arrest or punishment。

以下为相关双语示例：

An example of being an accessory before the fact might be giving a person the tools necessary to burglarize another person's home or a business. Another example would be giving someone the keys to a car to use in a robbery.

给予他人用于对另一人或企业进行入室抢劫工具的人属于事前从犯。给予他人车钥匙供他人在抢劫过程中使用的人也属于事前从犯。

In California, you can be charged with a crime if you help—in any way—a felon avoid getting in trouble. Helping someone who has committed a felony avoid the authorities or prosecution is referred to as being an accessory after the fact.

在加利福尼亚州，如果你以任何方式帮助重罪犯摆脱麻烦，则你可能会被指控犯罪。帮助犯有重罪的人逃避当局的搜捕或起诉的人一般被称为事后从犯。