Note: Liable is often interchangeable with likely in constructions with a following infinitive where the sense is that of probability: The Sox are liable (or likely) to sweep the Series. Some usage guides, however, say that liable can be used only in contexts in which the outcome is undesirable: The picnic is liable to be spoiled by rain. This use occurs often in formal writing but not to the exclusion of use in contexts in which the outcome is desirable: The drop in unemployment is liable to stimulate the economy. Apt may also be used in place of liable or likely in all the foregoing examples.
Libel: the legal tort of defamation, which occurs in the written word; defamation in the oral word is slander. Thus, one can be liable for libel.
Grammar.com’s section on Problem Words discusses apt, likely, and liable. Click here for that discussion.