It has become ubiquitous in the American culture to use “if” and “would” in the same phrase. It is especially prevalent among younger people just out of school or still in school, which makes me wonder, do their teachers say it, too, in their everyday speech?
You do not hear anyone over 50 saying, “If I would have known the item was on sale, I would have bought it today.” No one over 50 would say, “If they would have put up a sign, I would have found the place.” And certainly not, “I wish they would have told me.”
This use of the if/would combination implies an intention if given the opportunity; it does not mean that any action was taken or not taken.
“If I would have known” implies that I might have known, with a number of qualifications. It is indefinite at best. “If they would have put up a sign” makes me wonder what circumstances occurred to prevent them from carrying out their intention to put up a sign–if they had one. (They would have put up a sign, BUT…) And that is pure speculation. They might not have put up the sign even if they thought of it.
The solution to this dilemma is not to use “if” and “would” in the same phrase. You should say, “If I had known the item was on sale, I would have bought it today.” You should say, “If they had put up a sign, I would have found the place.” The element of intention is removed from the first part of the sentence: the point is that I didn’t know, and they didn’t put up the sign, so I didn’t buy the item and I didn’t find the place.
Let’s take the past participle off the shelf and give it back its rightful place, so that we who are over 50 don’t have to wince when we hear our children and grandchildren speak, or hear TV personalities speak. Don’t say, “I wish I would have known” when you mean, “I wish I had known.”
Oh, and by the way, how many times have you heard a speaker at a ceremony say, “I would like to thank so-and-so for this opportunity”? What’s stopping him or her from thanking so-and-so? It is no better to say, “I want to thank so-and-so.” Why not just come out and say the words, THANK YOU? Where’s our courage?