Certain sets of words in the English language tend to confuse people. I have found the following to be among them:
FREE / FOR FREE
The word free can be an adjective, a verb, or an adverb, but not a noun. What concerns us here is expansion of the single word free into the common expression for free. Since the word free, in this case, means without cost or charge, the preposition for used in conjunction with free is unnecessary and technically incorrect. Because free is not a noun, it cannot properly serve as the object of a preposition.
When you want to say that no cost is applied, free yourself of the preposition for, forgo the phrase for free, and feel free to just say free.
Incorrect: Buy one, and we’ll send you a second one for free.
Correct: Buy one, and we’ll send you a second one free.
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