"Purposely" Versus "Purposefully"
A memory trick for remembering the difference.
"Purposely" is the word you want when describing something done deliberately—done on purpose. If you know your sister is always late, you may purposely tell her the party starts 30 minutes earlier than it really does.
"Purposefully" describes the action or demeanor of a person who is determined or resolute. If you want to convey a message to your brother without speaking, you may purposefully raise your eyebrows.
Quick and Dirty Tip: Think of "purposefully" (purpose-full-y) as meaning “full of purpose."
Get more tips like this in The Grammar Devotional: