Just moments ago, I tested a little hypothesis of mine. First, I typed “I did it purposely” into Google. I got 14,100 hits. Reading through the first 10, I saw that all of them had used the word “purposely” correctly. I then searched for “I did it purposefully”. This time, I got 41,100 results. Nine out of the first 10 had misused “purposefully”, where “purposely” would have been the right choice.
So, not to brag, but my hypothesis was correct: “purposely” is almost always the right choice, but we use “purposefully” way more often. I have no idea why; I’m just a humble editor/research scientist.
I can, however, explain the difference between the two words:
“Purposely” means on purpose, intentionally:
I purposely missed the flight because I didn’t want to go.
She wouldn’t purposely hurt your feelings.
This page has been purposely left blank.
“Purposefully” means with purpose, in a purposeful way:
He spotted a police officer walking towards him purposefully.
It’s a good idea to set goals purposefully at the beginning of the year.
She widened her eyes purposefully, warning him not to answer.
Here’s a tip for keeping them straight: “purposefully” has the word “full” in it, and it means full of purpose. As well as remembering that, just keep in mind that “purposely” is a much more common concept. If in doubt, that’s probably the word you’re looking for.