Word Processing Grammar Checkers Miss More Errors Than They Find

If you've spent any time using e-mail, you probably have received a widely circulated limerick that lampoons the imperfections and limitations of spell-check software. It begins, "I have a spelling checker. / It came with my pea see. / It plane lee Marx four my revue / Miss steaks aye can knot sea." Although the spell-check functions built into word processing applications are effective in finding outright misspellings, they are unable to identify words that are spelled correctly but used mistakenly.
Word processors also have grammar-checking functions. Curious about how they perform, we tested a few with a little help from some of our friends — Tom Nefeldt, Jim Weske and Dave Williams.
Most grammar checkers use a technique called "natural language processing," which uses an integrated dictionary to identify the part or parts of speech of each word. That database — in theory — enables the grammar checker to "parse" sentences. Parsing is the process of dissecting a sentence into its component parts of speech while analyzing the function and syntactical relationship of each part .
The software parses sentences by applying grammatical rules written into the program — for verb tense and inflection, use of adjectives and adverbs, punctuation, subject-verb agreement and other conventions of grammar. Through that process, the program is supposed to determine whether a sentence is grammatically correct. In practice, however, the grammar-check applications that we tested overlooked far more errors than they found. In some cases, they made erroneous suggestions.
For the test, we prepared 40 sentences, each of which contains at least one error in grammar or word usage. Three of the sentences contain two errors apiece, and one sentence contains three errors, for a total of 45 mistakes. First see how many you can find, and then we'll tell you which errors the software found — and missed.

1. The Ohio State Buckeyes, they are practicing hard.
2. My class is in the mist of this project right now.
3. President Bush granting federal aid to much of Texas following wildfires which spread across the state.
4. Ralph did not complete the roof repairs on time, consequently, the rain damaged the living room ceiling.
5. Bob had hoped to find work in Albuquerque, but he accepted a job in El Paso out of shear necessity.
6. Water has been rushing through the levee since 3 a.m. this morning.
7. I apologize for the incontinence, and hope to have an opportunity to speak with you later.
8. By examining wear patterns on gears is how lubrication problems can be detected.
9. A youth hostile is like a residence hall.
10. Roger collected the data but Alice wrote the report.
11. Sheldon encouraged Stephanie and myself to apply for the grant.
12. The responsibilities of the vacant position includes online content management, site development, brand positioning, business development and contract negotiations.
13. Pasteurization is where milk is heated to a specific temperature for a certain amount of time to kill bacteria.
14. The pest control crew maybe fumigating the house on Monday.
15. The reason Robin left work early is because the heater was broken and the building was cold.
16. It is hoped that this measure will serve to compensate for sales tax revenues that were lower than anticipated.
17. The bus operates everyday except holidays.
18. Stephanie all ready submitted her report.
19. By your age I do not expect to have behavior problems in my class, I am a teacher not your baby-sitter.
20. Cayenne pepper contributes positively to the flavor of the dish.
21. Dallas/Fort Worth International Airport expects less passengers this Memorial Day.
22. Since Fred retired, he lays down and takes a nap on most afternoons.
23. The software upgrade will compliment our corporate customer relations management objectives.
24. Ellen is the person whom answered my question.
25. The puppy eats allot of dog food.
26. Gordon is already to sweep out the warehouse.
27. Have you considered always to ship the package?
28. The company has began the process of renovating the visitor lobby and conference rooms.
29. The principle cause of the fire was improper storage of cleaning solvents in close proximity to an electrical switching panel.
30. This fiscal year, Penny almost cut her department's travel expenses in half, and absenteeism is five times less than it had been two years ago.
31. The company's chief executive officer has formed a six-member advisory counsel to identify positive incentives to increase loyalty among employees.
32. Providence is one of the only cities in the United States that has an overnight parking ban.
33. "Don't dilute yourself into thinking this alleviates you of responsibility," Brian angrily told Phil.
34. The president nominated Frank and I to serve on the disciplinary review board.
35. By carefully following the steps in this recipe, your pork loin roast will be tender and moist.
36. Phyllis only took a 15-minute lunch break on Monday.
37. Mary told Carol to meet her at 4:15, but she missed the appointment because she forgot her watch.
38. It's disturbing what the Public Works Commission intends to do.
39. Farmers initially began using that insecticide in 1982.
40. The reason that Karen resigned was because she lost respect for her supervisor.

Our example sentences contain 18 types of errors:

• REDUNDANCY: sentences 1 (the pronoun "they" and the comma that precedes it should be deleted); 6 ("morning" and "a.m." are redundant); 20 ("positively" is superfluous with the verb "contributes"); 29 ("close" is redundant with "proximity"); 31 ("positive" is superfluous with "incentives"); and 39 ("initially" is superfluous with the verb "began")
• HOMOPHONE ERRORS: sentences 2 ("mist" should be "midst"); 5 ("shear" should be "sheer"); 9 ("hostile" should be "hostel"); 29 (the noun "principle" should be the adjective "principal"); 31 ("counsel" should be "council"); and 33 ("dilute" should be "delude")
• SENTENCE FRAGMENT: sentence 3 (lacks a complete verb)
• IMPROPER RESTRICTIVE PHRASE INTRODUCTION: sentence 3 ("which" should be "that")
• RUN-ON SENTENCE: sentences 4 (the comma after "time" should be a semicolon); and 19 (should be "...in my class; I am your teacher, not your babysitter")
• IMPROPER WORD CHOICE: sentences 7 ("incontinence" should be "inconvenience"); 14 (the adverb "maybe" should be the verb form "may be"); 21 ("less" should be "fewer," the proper adjective for use with plural-count nouns); 25 (the verb "allot" should be the phrase "a lot"); and 32 ("only" should be "few")
• FAULTY PREDICATION: sentences 8 (the prepositional phrase "by examining wear patterns on gears" cannot function as the sentence subject); 13 (should begin "Pasteurization is the process of heating milk"); 15 (should be either "Robin left work early because the heater was broken" or "The reason Robin left work early is that the heater was broken"); and 40 (the locution "the reason was" demands a "that" clause for completion)
• PUNCTUATION ERRORS: sentences 10 (a comma is missing before "but," the coordinating conjunction in this compound sentence); and 19 (a comma is missing before the contradictory element "not your babysitter")
• IMPROPER PRONOUN USE: sentences 11 ("myself" should be "me"); 24 (the subjective-case pronoun "whom" should be the nominative pronoun "who"); and 34 ("I" should be "me")
• SUBJECT-VERB DISAGREEMENT: sentence 12 (verb "includes" should be "include")
• PASSIVE VOICE: sentence 16 (requires proper subject, e.g., "The mayor hopes that this measure...")
• ADJECTIVE-ADVERB SWAP: sentences 17 (the adjective "everyday" should be the adverbial phrase "every day"); 18 (the adjective "all ready" should be the adverb "already"); 26 (the adverb "already" should be the adjective "all ready"); and 27 (the adverb "always" should be the adjective-noun combination "all ways")
• DANGLING PREPOSITIONAL PHRASE: sentences 19 (should be "By your age, you should be able to control your behavior..."); and 35 (should begin "If you follow the steps...")
• INCORRECT VERB: sentences 22 ("lays" should be "lies"); and 23 ("compliment" should be "complement")
• IMPROPER VERB INFLECTION: 28 ("has began" should be "has begun")
• MISPLACED MODIFIER: sentences 30 (the adjective "almost" should immediately precede "in half"); and 36 ("only" should appear immediately before "a 15-minute break" or before "on Monday," depending on intended emphasis)
• VAGUE PRONOUN REFERENCE: sentence 37 (who missed the appointment is unclear)
• AMBIGUOUS ANTECEDENT: sentence 38 (vague pronoun in this passive construction requires clarification about who is disturbed — e.g., "Lou finds the commission's intentions disturbing")

While the grammar checkers of the most popular word processing applications can help draw attention to problematic sentences, they don't always offer the correct reason or the proper resolution. In our test, the best-performing grammar checker found fewer than half of the errors in our example sentences. What word processing grammar checkers found — and missed:

Microsoft Word 2004 and 2008 for Macintosh correctly identified only eight of the 45 errors (18 percent of them), in sentences 4, 11, 12, 13, 16, 22, 28 and 40). It gave incorrect or misleading advice in eight instances: it suggested revising sentence 8, but for the wrong reason — calling it a passive construction rather than identifying the problem as faulty predication; in sentence 3, in which it suggested replacing the proper preposition "to" with the adverb "too"; in sentence 14, which it misinterpreted as a sentence fragment; in 21, in which it suggested changing the "w" in "Fort Worth" to lowercase; in 23, in which it missed the homonym error and incorrectly suggested changing "relations" to the possessive form "relation's"; in sentence 27, in which it missed "all ways," but suggested replacing "to ship" with "shipping" — thereby changing the intended meaning of the sentence; in 33, in which it missed the "dilute" error, yet made the inconsequential suggestion to change "don't" to "do not"; and in 38, in which it overlooked the ambiguous antecedent while suggesting replacement of "it's" with "it is").

Microsoft Word 2007 for Windows found 11 errors (24 percent of them), in sentences 3, 4, 9, 11, 12, 17, 22, 23, 28 and 31. While it correctly identified the "less/fewer" problem in sentence 21, it incorrectly recommended using a lowercase "w" in "Fort Worth." It also gave incorrect advice in sentence 27, in which it missed "all ways," but suggested replacing "to ship" with "shipping" — thereby changing the intended meaning of the sentence.

WordPerfect Office X4 did the best job; it correctly identified 21 errors (48 percent), in sentences 8, 12, 15, 16, 17, 18, 21, 24, 26, 28, 31, 32, 34 and 40. It also correctly identified both errors in sentences 3 and 29. It identified the run-on problem and the missing comma before the contradictory "not" in sentence 19, but overlooked the dangling prepositional phrase; and in 23 it correctly recommended changing "compliment" to "complement," but incorrectly suggested changing "customer" to the possessive form "customer's". It gave incorrect or misleading advice in eight other instances: in sentence 5, it misunderstood the idiomatic expression "out of ... necessity" and incorrectly recommended changing "shear" to "shearing"; in 6, it missed the "a.m."/"morning" redundancy, yet made the inconsequential suggestion to change "3 a.m." to "3:00 a.m."; for sentence 9, it suggested moving "hostile" before youth (thereby altering intended meaning), and changing "residence" to "home" or "house"; it suggested revising sentence 13, but for the wrong reason — calling it a passive construction rather than identifying the problem as faulty predication; it misinterpreted 14 as a sentence fragment; in 25, it missed the problem with "allot" and incorrectly disputed use of the verb "eats"; in 33, it missed the "dilute" problem while suggesting replacement of the contraction "don't" — a superficial change; and in 38, it suggested replacing "it's" with "it is" or "it has."

All of the grammar checkers overlooked errors or offered incorrect suggestions in 17 sentences: 1, 2, 5, 6, 7, 10, 14, 20, 25, 27, 30, 33, 35, 36, 37, 38 and 39.
The ability of grammar-checking software to function at even a rudimentary level is remarkable, because the English language is pockmarked with so many exceptions to rules and with idiomatic phrases that defy literal translation and have their own distinct syntax. Asking a computer application to analyze the English language with all its idiosyncrasies, and to rectify errors in usage, is an unreasonable request.
Use software grammar checkers with discretion, therefore. Editing for proper grammar is one function in which humans still vastly outperform computers.