Of all of the Latin terms that have reached common use, “per se” suffers the most misspelling. Because “se” is not a word in English, people insist on “correcting” it to "say". Let's take at what the individual words mean and hope that it will help people remember how to spell and use it.
In Latin, per means “through” or “by means of”. You can use it with units of time, such as per diem or per annum meaning daily or yearly, and with parts of the body, like per os (by mouth, indicating how you take a medication) or per pedes (by foot or as a pedestrian).
Se simply acts as a reflexive pronoun, regardless of number or gender. It takes the place of herself, himself, itself, and themselves. A handy tool for a writer to have, don't you think?
Let's try an example.
Necessity is not the mother of invention per se. It requires inspiration to complete the creation.In this case, you could write, “Necessity is not the mother of invention by itself,” or, “Necessity, alone, is not the mother of invention.” Either would capture the meaning of the Latin phrase.
Now that you know what it means, please do not hesitate to use it. The correct spelling will not make its way into the world per se, you know. It needs you to help show others the way.