At work the other day I did a search for a windows version of vi, a text editor. I searched “vi for windows” (without quotes) and a this site was the first result. Later on that day, I searched “vi windows” (again without quotes) and a different site was the number one result. The funny thing is that in the first search, Google claimed to disregard the “for” because it was a common word. I decided to see what would happen if I threw in random common words like and, the, a, etc. It gave me the same results as using “for,” so it seems as though Google disregards what the word is, but having a common word there does affect the search results. I know Google gives higher preference to sites with the words together, so maybe search #2 likes sites with “vi windows” right next to each other whereas search #1 doesn’t give extra credit for proximity. The common word acts as a barrier.