He was educated at Eastwood High School and the University of Glasgow.
In 1989, he was appointed a Senator of the College of Justice, taking the title Lord Caplan.
During his tenure, Caplan was one of the two Jewish judges on the Scottish High Court bench, alongside Hazel Cosgrove, Lady Cosgrove.
[2] As a judge, Caplan heard what was then Scotland's longest civil case, which ran over 391 days, concerning the explosion of the oil platform Piper Alpha.
In 1997, he issued a 1,500 page judgment which blamed the explosion on two dead platform workers, contradicting the report of Lord Cullen, which had blamed the platform's operator.