Many teachers, test designers, textbook writers, and instructional designers turn to books written by usage experts to determine what is correct standard written American English. Unfortunately, though, experts often disagree about what is correct and what is incorrect, and this disagreement can create problems with validity when people create and assess instruction about usage. One way to discover the rules of standard English usage is to describe what writers actually do in printed, edited English. Researchers can access large collections of standard English through digital text archives, which can be searched electronically. The text archives for this study were taken from EBSCO and ProQuest digital libraries and divided into three different registers: (a) newspapers, (b) magazines, and (c) scholarly journals. This study examines 30 representative items of controversial usage; such as "a lot" or "alot," "between you and I" or "between you and me," "had proved" or "had proven"; to determine the actual occurrence in these three registers of standard written American English. The results list the percentage of use in each register, as well as the total averaged percentage of use in all three registers. Items showing 90% to 100% usage in the total averaged percentages are considered standard English, but items showing 90% to 95% usage are borderline cases that should be monitored for future use. If a variant form is used more than 10% of the time, then it should be considered a possible alternative usage in dictionaries, in text books, and in tests. This study shows the results of using corpus linguistics to answer questions about usage in standard American English.