Complex sentence: Arthur Johnston (1587-1641) was a Scottish physician and poet, and a son of Aberdeenshire laird, Johnston of Johnston and Caskieben, and a grandson, on his mother's side, of the seventh Lord Forbes.
Split into simpler sentences: Arthur Johnston (1587-1641) was a Scottish physician and poet. He was he son of an Aberdeenshire laird, Johnston of Johnston and Caskieben, and on his mother's side a grandson of the seventh Lord Forbes.