When are liable and likely interchangeable?

Question

For liable, a sentence in which it is used correctly;

Such a figure is liable to be attacked as a blasphemer.

For likely:

What he told me is likely to be true. (Not liable. It sounds weird)

Ok I know I can't be 100% sure of things just because of how it sounds. I want a reason from a grammatical view point.

Here is a sentence where liable is less suitable than likely. (According to my exam practice book. It doesn't explain why. But its words definitely got some weight to it.)

That book is liable to become a best seller because it is well written, full of suspense, and very entertaining,

Answer 1

'Liable' means (in one sense), 'open to', 'capable of', with no necessary connotation of the likelihood or probability of the event. So, "Such a figure is open to/capable of being [= liable to be] attacked ....".

'Likely', on the other hand, so far as I can imagine right now, always suggests a connotation of probability (likelihood). So, "What he told me is probably [= likely to be] true."

In your third example, the context makes it clear that the 'likely' sense of liable is being used, rather than the 'capable of' sense: any book (much as I hate to admit it) is 'capable of' becoming a best seller, so a reader of the sentence understands the sense of 'liable' used is not merely 'open to/capable of' (that being understood) but 'likely to'.

liable

adj.

....

3. probable, likely, or capable

(from The Free Dictionary, italics mine)

Then, 'capable' (adj.):

1. Having capacity or ability ....

(op. cit.)

Observe that stating the capacity exists is materially different than stating the capacity will be realized.

See also the usage note concerning 'liable':

Usage: The use of liable to to mean likely to was formerly considered incorrect, but is now acceptable.

(op. cit.)

Edit

Your edit of the question puts a slightly different complexion on the third example. The list of reasons in the example make it more than abundantly clear that 'likely to' is the sense used. For this reason, the preferable choice of terms is 'likely', rather than 'capable', because 'likely' is the more precise term for communicating that meaning.

Answer 2

The reason for this is that liable has negative implications. From The American Dictionary of the English Language by Noah Webster we have this usage note for this sense of the word:

Liable, in this sense, is always applied to evils. We never say, a man is liable to happiness or prosperity, but he is liable to disease, calamities, censure; he is liable to err, to sin, to fall.

However, the definition I'll give is rom the Century Dictionary and Cyclopedia 1890-1914 since it's a little more direct:

Having an aptitude or tendency; subject; exposed, as to the doing or occurring of something evil, injurious, or erroneous: as, we are constantly liable to accidents; your plans are liable to defeat.

This doesn't really seem to indicate that liable is very likely but perhaps more probable than not or at least more probable than desired. The American Heritage Dictionary, 5th Edition does liken the word to likely though and notes that liable in the sense of likeliness should be reserved for when the subject is likely to experience an unfavorable outcome. The only time you'd say liable like this is 'Springtime for Hitler is liable to become a huge success.' Otherwise, being a bestseller would be a good thing. That's the main reason why it's considered wrong: Liable is reserved for emphasizing potential problems and bad consequences.

I have further speculations through synonymy with the idea that it must happen, referencing the sense of being "bound" as A.D.E.L. and C.D.C. state in their primary sense of legal obligation. If it is bound to happen, it must happen as if it is destined since it is limited to that outcome alone. See some of the 2010 Random House Kernerman Webster's College Dictionary's definitions of bound definitions for that sense. "This book is bound to become a bestseller." is certainly a statement I've seen in marketing sometimes and "This book is liable to become a bestseller" is occasionally used in its place. However this paragraph is mostly just doubtful guesswork..

Answer 3

I have always interpreted that "liable" formally implied "legal responsibility" for one's actions when they cause damage to people, or people's property, so that compensation or even punishment would be required if the case were to be judged by an authorised "party". In my case of learning &understanding "liable" I never included any aspect of "probability". The information presented in the texts above seems to indicate an entirely different meaning now-a days that has nothing to do with legal responsibility and accountability!