apt

apt, liable, prone

1. Used with to, prone is by far the most common statistically, liable comes second, and apt, perhaps surprisingly, trails in third place.

2. Apt to and liable to, followed by an infinitive, are virtually interchangeable, except that liable carries a greater notion of responsibility for the result, which is generally implied to be undesirable. Examples:

• Pick up any ‘documentation’…and you are apt to be…bombarded by gibberish —New York Times, 1982

• Given that it's the exam season, I'm apt to be distracted by just about anything —weblog, BrE 2005 [OEC].

In this use, apt to is tending to force out the alternative prone to, although this is still used in relation to habits and continual actions:

• The one unquestionable advantage of the multiflora stock is the fact that it is less prone to throw up suckers than any of the others —N. Young, 1971.

3. Liable to and prone to, unlike apt to, can be followed by a simple object, and in this use liable to also has the meaning ‘subject to (a penalty)’:

• The affected children themselves are liable to behavioural problems such as temper tantrums —Journal of the Royal Society of Medicine, 1980

• Anyone convicted of giving away examination papers to candidates will be liable to two years in jail —Daily Telegraph, 1982.

Both words can usefully be followed by a verbal noun in -ing

• (EB…makes her skin as fragile as a butterfly's wing and prone to blistering —Manchester Evening News, 2003).

4. Likely to, followed by an infinitive, is more neutral than the other words in fitting well into favourable as well as unfavourable contexts. It is also far more common than the other three put together:

• A plan to help young home-buyers is likely to be announced within the next week —Times, 1973

• For the parents of teenagers who are likely to have encounters with the police, the teenage years can be a nightmare —BBC Parenting, 2004.