The Top 20 Language Mechanics and Number Expression Rules Used in Technical Writing

1. Use a comma before a coordinating conjunction that joins two independent clauses. Hint: coordinating conjunctions are FANBOYS (for, and, nor, but, or, yet, so).

   • We spent hours discussing solutions to the problem, but we failed to decide on a course of action.

   If a sentence contains both an independent and dependent clause, no comma is needed.

   • The committee plans to collect the data by March but will not have the report completed until June.

2. Use a comma after introductory words, phrases, and clauses.

   • On the basis of the CEO’s recommendations, we decided to expand our operations.
   • Arriving late to class, Olivia had trouble finding a seat.
   • To find a seat in class, I recommend you arrive 5 min early.

3. Sentence fragments occur when dependent clauses are written as complete sentences. Connect dependent clauses to independent clauses to form a complete sentence.

   • Incorrect: Based on 2010 data.
   • Correct: The controller provided a cost estimate that was based on 2010 data.

4. Use commas between words, phrases, or clauses appearing in a list of three or more including a comma before the coordinating conjunction. The Oxford/serial comma is used in technical writing.

   • Four popular Internet search sites are Google, Bing, Yahoo, and Ask.

5. Transitional words and phrases improve the flow of sentences and help guide the reader. Transitional words can be used at the beginning, middle, or end of sentences and are set off with commas.

   • Therefore, the results appeared to have effects that were not predicted.
   • You should, nevertheless, continue to master grammar rules.
   • The average world temperature has continued to rise significantly, however.

6. When a transitional word (however, furthermore, consequently, therefore, moreover, etc.) joins two independent clauses, place a semicolon after the first independent clause and a comma after the transitional word or omit the transitional word and comma and place a semicolon between the two independent clauses.

   • Departments will have budget increases; therefore, staff will receive all equipment requested. OR
   • Departments will have budget increases; staff members will receive all equipment requested.

7. A run-on sentence occurs when two independent clauses are placed together without a conjunction or punctuation mark joining the clauses. A comma splice occurs when two independent clauses are separated with a comma. Punctuate both run-on sentences and comma splices by adding a semicolon or a comma and conjunction between the independent clauses.

   • Incorrect: The company performed well last quarter its stock rose several points. (run-on sentence)
   • Incorrect: The company performed well last quarter, its stock rose several points. (comma splice)
   • Correct: The company performed well last quarter; its stock rose several points.
   • Correct: The company performed well last quarter, so its stock rose several points.

8. An appositive is a noun or noun phrase that renames or describes another noun or pronoun in a sentence. Appositives essential to the meaning of the sentence are not set off with commas; appositives non-essential to the meaning of the sentence are set off with commas.

   • My friend John just ran his first marathon. (essential)
   • Pahoehoe lava, a textured formation, occurs on the Kilauea volcano in Hawaii. (non-essential)

9. Use commas to set off words, phrases, and clauses non-essential to the meaning of the sentence.

   • My son, who plays the piano beautifully, is studying abroad.

   Commas are not used to set off words, phrases, and clauses essential to the meaning of the sentence.

   • The man who backed his car into my car drove away without stopping.

   NOTE: Clauses that begin with that are considered essential to the meaning of the sentence and are not set off with a comma. Clauses that begin with which are considered non-essential to the meaning of the sentence and are set off with a comma.

   • The book that you ordered yesterday is no longer available for purchase. (essential)
   • Please use the credit card in my wallet, which is on the dresser. (non-essential)

10. Use a comma between related adjectives that precede a noun.

    • His direct, practical approach has created a high degree of respect.

11. Use commas to set off geographic names, complete dates (month/day/year), and titles in names. Avoid abbreviating names of states in sentences.

    • Birmingham, Alabama, was the first manufacturing city in the world.
    • July 22, 1959, was a momentous day in his life.
    • The average temperatures for July 1998 are the highest on record.
    • The keynote speaker is Rachel B. Lake, PE.

12. Achieve parallel structure by using the same pattern of words to improve the flow of the sentence and to show that two or more ideas (words, phrases, or clauses) have the same level of importance.

    • Incorrect: In his free time, Fred likes to read, hike, and watching birds.
    • Correct: In his free time, Fred likes to read, hike, and watch birds.
    • Correct: In his free time, Fred likes reading, hiking, and watching birds.

13. Add ’s to the singular form of a noun to make it possessive; add s’ to the plural form of a noun to make it possessive; and add ’s to the end of a compound noun.

    • The boy’s hat is green.
    • The three girls’ sweaters are identical.
    • Todd and Anne’s house is heated geothermally.

    Add an ’s to possessive nouns naturally ending in s. Certain style guides suggest omitting the extra s and only adding an apostrophe.

    • Moses’s hat is green. OR
    • Moses’ hat is green.

    No apostrophe is used with plural numbers, symbols, and letters.

    • The 1960s were a time of social unrest.
    • The printed page has too many &s on it.
    • There are four Ss in Mississippi.

14. Unclear pronoun reference occurs when a pronoun (it, this, that, them, they) refers to more than one noun in the sentence. Unless the reference is obvious, re-state the noun being referred to.

    • Incorrect: Transmitting radio signals by satellite is a way of overcoming the problem of scarce airwaves and limiting how they are used.
    • Correct: Transmitting radio signals by satellite is a way of overcoming the problem of scarce airwaves and limiting how these signals are used.

15. Avoid misplaced or dangling modifiers by placing the phrase or clause near the word it modifies.

    • Incorrect: He bought a horse for his sister named Prince.
    • Correct: He bought a horse named Prince for his sister.

16. Avoid mistakes that occur when words sound alike but have different meanings or spellings (homophones). Examples include affect/effect, our/are, to/two/too, their/they’re/there, principle/principal.

    • The weather conditions will affect the number of people who ski this year. (Affect means to influence something and is typically a verb.)
    • What effect did the loss have on the team? (Effect indicates a result and is typically a noun.)

17. Use a colon after an independent clause when introducing a list.

    • We covered three fundamentals in our technical writing class: grammar, style, and voice.

    NOTE: If the clause following the colon is an independent clause, capitalize the first word.

    • Researchers have agreed on the outcome: Informed participants are more likely to participate in medical trials.

18. Place periods and commas inside quotation marks.

    • He said, "I may forget your name, but I never forget a face."

    If the quote is phrased as a question, place the question mark inside the quotation marks.

    • She asked her classmate, “May I borrow a pencil?”

    NOTE: Use italics rather than quotation marks to emphasize words in a sentence.

    • Why am I always the last to know?

19. Subjects and verbs must agree in number. If the subject is singular, the verb should be singular. If the subject is plural, the verb should be plural.

    • In the past three months, a new line of inexpensive computers has been released.
    • In the past three months, two new lines of inexpensive computers have been released.

20. The following number-related rules comply with generally accepted technical writing standards. Rules may differ based on discipline; consult a discipline-specific style manual for number and unit expression.

A. Number Expression

Spell out single-digit numbers zero through nine, except for measured quantities. Numbers 10 or greater are expressed numerically. For numbers in the millions, billions, or trillions, use the number followed by million, billion, or trillion.

• The collision damaged seven vehicles and injured four passengers.
• The project will take between 12 and 14 months to finish.
• Flying to Kepler-452b would take 28 million years.

If a sentence contains related numbers that are both less than and greater than 10, express all numerically.

• The farmer bought 4 chickens, 12 pigs, and 9 goats.

Approximate numbers follow the same rules as exact numbers.

• About 50,000 discrete events were recorded.
• Approximately 8 samples in 20 had to be discarded.

Avoid starting sentences with numbers; either spell out the number or revise the sentence.

• Incorrect: 25 engineers were involved in the project.
• Correct: Twenty-five engineers were involved in the project. OR The project involved 25 engineers.

B. Units and Abbreviations

If a number is followed by a unit of measurement, abbreviate the unit and leave one space between the number and the unit. For numbers less than 1.0, insert a zero to the left of the decimal point.

NOTE: A period is included after the abbreviation for ínch (in.) to differentiate from in used as a preposition.

• The heat transfer surface of the cylinder was covered with 25 mm of insulation.
• Salt Lake City received 9.3 in. of snow on January 8, 2019.
• On Tuesday, there is a 0.001 chance of rain.

To prevent misreading, do not abbreviate the following units of time even when they are accompanied by a numeric value: day, week, month, year. All other units of time are abbreviated: hour = hr or h; minute = min; second = s or sec; millisecond = ms or msec; nanosecond = ns or nsec.

• The gestation period for an African bush elephant is 22 months.
• Students are allowed 50 min on the exam.

Symbols for units are written in the singular form.

• There are 1000 mm in 1 L. NOT There are 1000 mms in 1 L.

If the unit of measurement is named for a person, the unit is capitalized.

• The strength of an average solar sunspot is equal to 0.3 T.
• The technician heated the sample to 80 °C

NOTE: In a non-numeric context, spell out the unit and use a lower-case first letter (even if the unit is named for a person).

• A tesla is a unit of measurement of the strength of a magnetic field.

Write secondary/converted units in parentheses after primary units.

• Please install a 2-in. (5.08-cm) rod.

NOTE: Place a hyphen between numbers and units used to modify a noun.

• Civil engineering students are invited to a 3-day conference.

C. Non-Measured Amounts

Numerals are used to represent certain non-measured amounts.

• Time: The event runs from 9 to 11:30 a.m.
• Age: Children typically start kindergarten at the age of 5.
• Points on a scale: The most popular points on a Likert scale are 5 or 7.
• References to figures and tables: Figure 4 illustrates the increase in attendance over a 5-year period.
• Percentages: Attendance dropped by 45.2%.
• Money: $0.26, $1.1 million, $60.12, $45 (For whole dollar amounts, exclude decimals and zeros.)

D. Fractions and Decimals

Spell out and hyphenate simple, isolated fractions. Use numerals and a forward slash for more complicated fractions.

• The candidate won by a two-thirds majority.
• The mixture required 18/25 of the total volume.

When the precise value of a fraction is required, use the decimal form.

• The technician added 0.5 L to the mixture.

E. Adjacent Numbers

When two numbers are adjacent, retain the number that goes with the unit and spell out the adjacent number.

• The technician ordered twelve 26-in. pieces.

If the first number is complicated to express numerically, spell out the number that goes with the unit.

• The technician ordered 4,256 twenty-six-in. pieces.