Many of today's grammar rules can be traced to the opinions of one 18th century writer.
A definitive answer.
The most common vowel sound in English causes many spelling problems.
Is 'alright' all right?
A simple trick to keep them separate
'Poets laureate'? 'Court-martials'? The curious history of postpositive adjectives in English.
A simple way to keep them apart. (Most of the time.)