Different versions of this idiom have been used since the 1600’s. The exact origin of this idiom is not known but it could be linked to how difficult it would be to ‘split’ or divide a hair. Also, doing this would be pointless! Why would we split a hair! From this, it seems that splitting hairs would be difficult and pointless so we use this expression to mean arguing about small and meaningless details. In the past, other versions of this idiom have included ‘to cut a hair’ and ‘it’s hard to split the hair.’ We only use ‘to split hairs’ now though. Try to use this the next time you have an argument with someone you think is being unreasonable – it works very well!