¹open

frank, candid, open, plain mean showing willingness to tell what one feels or thinks. frank stresses lack of shyness or secretiveness or of evasiveness from considerations of tact or expedience <frank discussions>. candid suggests expression marked by sincerity and honesty especially in offering unwelcome criticism or opinion <a candid appraisal>. open implies frankness but suggests more indiscretion than frank and less earnestness than candid <open in saying what they think>. plain suggests outspokenness and freedom from affectation or subtlety in expression <plain talk>.

liable, open, exposed, subject, prone, susceptible, sensitive mean being by nature or through circumstances likely to experience something adverse. liable implies a possibility or probability of incurring something because of position, nature, or particular situation <liable to get lost>. open stresses a lack of barriers preventing incurrence <a claim open to question>. exposed suggests lack of protection or powers of resistance against something actually present or threatening <exposed to infection>. subject implies an openness for any reason to something that must be suffered or undergone <all reports are subject to review>. prone stresses natural tendency or propensity to incur something <prone to delay>. susceptible implies conditions existing in one's nature or individual constitution that make incurrence probable <very susceptible to flattery>. sensitive implies a readiness to respond to or be influenced by forces or stimuli <unduly sensitive to criticism>.

Both liable and apt when followed by an infinitive are used nearly interchangeably with likely. Although conflicting advice has been given over the years, most current commentators accept apt when so used. They generally recommend limiting liable to situations having an undesirable outcome, and our evidence shows that in edited writing it is more often so used than not.