How would you classify language as being used by a single individual? As an individual's language is formed from a unique combination of sociolect, dialect and idiomatic influences.
Do idiolects even exist and if so, how do other people understand them if it is unique to that individual?
Furthermore, idiom is defined a "a form of figurative expression that is particular to a certain person or group of people."
According to my poetry teacher, Seamus Heaney uses idiolects:
By God, the old man could handle a spade. Just like his old man.
Would the noun phrase 'old man' be an idiolect here? (I've heard Americans use 'old man' or 'pops' on television before). And, would the idiom here be, 'the old man could handle a spade'?