Neither et al. nor etc. have entries in the AP Stylebook. That does not mean that they are not allowed under AP Style per se, because the main rule of AP Style is to use Webster’s Dictionary unless there is an overriding rule provided in the Associated Press Stylebook. That would make both et al. and etc. permissible as words and/or abbreviations included within Webster’s, but it still doesn’t bode well for our heroes.
It isn’t that writing that contains et al. or etc. is bad writing, it’s just that it is completely possible to construct meaningful sentences without using them. In fact, in most cases, it is probably preferable not to use them since both are badly overused, and technically speaking, they have definite meanings and specific usages that often do not apply in the cases they are used. More specifically, etc. is NOT to be used to complete a clause that starts with such as or for example.
To use etcetera in a sentence is to imply that the the reader already knows the rest of the set it is referring to, not, as it is so often used, as a placeholder for an undefined set. (Note that etc. is fine to use when referring to an infinite set, which is, by definition, a known set.)
When To Use Etc. and Et Al. in Professional Writing
I find my motivation low today. When that happens, I fall back on all the usual writing hacks including overusing terms that may be freely used in popular lexicon, but impractical or improper in formal writing. Thus, I went to the freelance writer‘s trusty companion AP Stylebook to guide me on the usage of either etc. or et al. and have come away realizing that what is actually in order is a rewrite.
Write well, friends.