Comparing "henduo" and "xuduo"

很多 and 许多 both are number words that mean a lot, many, or much and often can be used interchangeably. Both are used in informal and formal situations. The key to understanding 很多 and 许多 is that when they are used as an object after a verb, or when attributed to something that you have a lot of, for example friends, things, etc., they can be used interchangeably. A difference is that only 很多 can be the predicate of a sentence.

注：汉语近义词学习手册的解释很不错，涉及到很多语法方面的内容。