The prefix con- (and its twin com-) has two pronunciations in American English, and the only thing that decides between them is stress. When con-/com- is unstressed, it shrinks to a quick /kən/ or /kəm/ ("k'n", "k'm"), as in conTROL and comPUter; when it is stressed, it opens up to /kɑn/ or /kɑm/ with the "ah" of father, as in CONtact and COMmon.
That is the whole rule. Spelling does not help you here, because control and contact start with exactly the same four letters. What helps you is knowing where the stress falls. Once you know that, the vowel takes care of itself.
The rule
- Unstressed con-/com- = schwa. /kən/, /kəm/: connect /kəˈnɛkt/, control /kənˈtroʊl/, complete /kəmˈplit/, computer /kəmˈpjut̬ɚ/.
- Stressed con-/com- (primary or secondary stress) = /ɑ/. /kɑn/, /kɑm/: contact /ˈkɑntækt/, concert /ˈkɑnsɚt/, conversation /ˌkɑnvɚˈseɪʃən/.
Think of it as "k'n" versus "KAHN". The first is a tiny, weak beat that leads into the stressed syllable. The second is a full, open, loud syllable that carries the word.
Why it works
English is a stress-timed language. Stressed syllables are long and clear; unstressed syllables are squeezed short, and their vowels usually collapse into schwa /ə/, the most relaxed vowel in the language. You can read more about this in our guide to the schwa and unstressed syllables.
The prefix con-/com- is just a very common victim of this process. It came into English from Latin, where it meant "with" or "together" (think connect = tie together, combine = put together). In modern English, speakers no longer feel it as a separate piece, so it behaves like any other syllable: if the stress lands on it, it gets a full vowel; if the stress lands somewhere else, it reduces.
Why /ɑ/ and not /oʊ/ or /ɔ/? In American English, the letter o in a stressed closed syllable (followed by a consonant in the same syllable) usually has the "lot" vowel, which for most Americans is the same as the vowel in father: /ɑ/. So con rhymes with John and Don, not with cone. (British speakers use a rounded /ɒ/ here, but this site follows American English.)
Pattern examples
Read each column out loud. On the left, the prefix is weak and fast, and the stress hits the next syllable. On the right, the prefix is the stressed syllable.
| Unstressed: /kən/, /kəm/ | IPA | Stressed: /kɑn/, /kɑm/ | IPA |
|---|---|---|---|
| conNECT | /kəˈnɛkt/ | CONtact | /ˈkɑntækt/ |
| conTROL | /kənˈtroʊl/ | CONcert | /ˈkɑnsɚt/ |
| comPLETE | /kəmˈplit/ | COMment | /ˈkɑmɛnt/ |
| comPUter | /kəmˈpjut̬ɚ/ | COMmon | /ˈkɑmən/ |
| comPARE | /kəmˈpɛr/ | COMpliment | /ˈkɑmpləmənt/ |
| conCERN | /kənˈsɝn/ | CONcept | /ˈkɑnsɛpt/ |
| conFUSE | /kənˈfjuz/ | CONference | /ˈkɑnfərəns/ |
| conSIder | /kənˈsɪdɚ/ | CONfident | /ˈkɑnfədənt/ |
| comMIT | /kəˈmɪt/ | CONverSAtion | /ˌkɑnvɚˈseɪʃən/ |
| conTINue | /kənˈtɪnju/ | COMbiNAtion | /ˌkɑmbəˈneɪʃən/ |
Notice the last two words on the right. Conversation and combination have their main stress later in the word, but con-/com- still carries a secondary stress (a smaller beat). That secondary stress is enough to keep the full /ɑ/: KAHN-ver-SAY-shun, not k'n-ver-SAY-shun.
One small bonus: before /k/ and /ɡ/, the n usually becomes /ŋ/ (the sound in sing). That is why congress is /ˈkɑŋɡrəs/ and conquer is /ˈkɑŋkɚ/. Your tongue simply gets ready for the next consonant.
Noun vs verb pairs
Many two-syllable con- words are both a noun and a verb. As in record and present, the noun is stressed on the first syllable and the verb on the second (see our post on noun-verb stress shift). Because the stress moves, the vowel of con- changes too:
| Word | Noun (or adjective): CON- | Verb: con- |
|---|---|---|
| contract | /ˈkɑntrækt/ a legal agreement | /kənˈtrækt/ to shrink; to catch (a disease) |
| conduct | /ˈkɑndʌkt/ behavior | /kənˈdʌkt/ to lead, to direct |
| conflict | /ˈkɑnflɪkt/ a fight, a clash | /kənˈflɪkt/ to disagree, to clash |
| contest | /ˈkɑntɛst/ a competition | /kənˈtɛst/ to challenge |
| convert | /ˈkɑnvɝt/ a person who changed beliefs | /kənˈvɝt/ to change into |
| convict | /ˈkɑnvɪkt/ a prisoner | /kənˈvɪkt/ to find guilty |
| combine | /ˈkɑmbaɪn/ a farm harvesting machine | /kəmˈbaɪn/ to mix together |
| console | /ˈkɑnsoʊl/ a control panel, a game system | /kənˈsoʊl/ to comfort |
| content | /ˈkɑntɛnt/ what is inside (noun) | /kənˈtɛnt/ satisfied (adjective) |
So "I read the CONtract" has /ˈkɑn-/, but "Metal will conTRACT in the cold" has /kən-/. Be aware that American speakers vary on a few of these verbs. For example, many people also say CONtract for the verb "to make an agreement", and you will hear both stresses for the verb conflict. The noun forms, however, are very stable.
Word families: the vowel follows the stress
Adding a suffix often moves the stress, and the con-/com- vowel changes with it. These pairs are a great way to hear the rule in action:
| Stress on con-/com- | Stress moves away |
|---|---|
| CONfident /ˈkɑnfədənt/ | conFIDE /kənˈfaɪd/ |
| CONference /ˈkɑnfərəns/ | conFER /kənˈfɝ/ |
| COMbiNAtion /ˌkɑmbəˈneɪʃən/ | comBINE /kəmˈbaɪn/ |
| COMpeTItion /ˌkɑmpəˈtɪʃən/ | comPETE /kəmˈpit/ |
| CONsulTAtion /ˌkɑnsəlˈteɪʃən/ | conSULT /kənˈsʌlt/ |
| COMparable /ˈkɑmpərəbəl/ | comPARE /kəmˈpɛr/ |
Same prefix, same root, different vowel. You do not need to memorize both forms separately; just find the stress and apply the rule.
Exceptions: when stressed com-/con- sounds like "cum"
There is one well-known group where a stressed com- does not use /ɑ/. Instead, the o is pronounced /ʌ/, the vowel of cup:
- company /ˈkʌmpəni/ (not "KAHM-pa-nee")
- comfort /ˈkʌmfɚt/
- comfortable /ˈkʌmftɚbəl/ (often three syllables: "KUMF-ter-bul")
- compass /ˈkʌmpəs/
These belong to the old spelling pattern where o is written but /ʌ/ is said, as in love, son, and money. Our guide to when O says U covers the whole family. The word conjure is usually /ˈkɑndʒɚ/ in the US, although some speakers say it with /ʌ/.
How to spot them: they are short, everyday, very old words, and most of them are spelled com- followed by p or f. When a stressed com-/con- word feels basic and common, and you are not sure, check a dictionary. For almost everything else, stressed means /ɑ/.
Also be careful with look-alikes that are not the prefix at all: come /kʌm/, become /bɪˈkʌm/, comb /koʊm/, and cone /koʊn/ follow their own spelling rules.
Common mistakes for learners
1. Saying every con- as a full "kon"
Many languages have a prefix that looks the same: Spanish and Portuguese con-, French con-, German Kon-. In those languages it usually keeps a full vowel. Carried into English, this makes control, computer, and connect sound heavy and robotic: "KOHN-trol" or "kon-TROL" with two strong beats. The natural American version is "k'n-TROL", with the first syllable almost swallowed.
2. Putting stress in the wrong place
A full vowel on con- pulls the listener's ear toward that syllable, so it can sound as if you are stressing it. If you say "KON-cern" instead of conCERN, the word becomes harder to recognize. On the other hand, cognates like contact, concert, and conflict are often stressed on the second syllable in other languages, but English stresses them on the first.
3. Nasalizing instead of pronouncing /n/ or /m/
French and Portuguese speakers often turn con into a nasal vowel with no real consonant. In English, /n/ is a full consonant: the tip of the tongue touches the ridge behind the upper teeth. /m/ needs both lips to close. Make that contact clearly, especially before a vowel, as in connect /kəˈnɛkt/ and commit /kəˈmɪt/.
4. Using a rounded "o" for the stressed version
For stressed con-/com-, open your mouth and relax your lips: /ɑ/ as in father, not a tight, rounded "o". Concert is "KAHN-sert", not "KONE-sert".
Practice
Listen and repeat each word. First decide: is con-/com- stressed or not? Then choose /kən/ or /kɑn/.
Sentences
Mark the stressed syllables, then read each sentence aloud. The weak /kən/, /kəm/ forms are in italics; the strong /kɑn/, /kɑm/ forms are in bold.
- Please contact me if you can't connect to the network.
- The computer will compare the two files.
- I'm confident the concert will continue after the break.
- We had a conversation about the new contract.
- Don't confuse the content of the report with the conclusion.
- The company made the office more comfortable. (Both are the /ʌ/ exception: "KUM".)
Did you catch the trap in sentence 5? Conclusion looks like it might start strong, but the stress is conCLUsion, so it is /kənˈkluʒən/ with a weak /kən/. Always check the stress before you choose the vowel.
Beyond con-: the same logic in other prefixes
The stress-controls-the-vowel rule is not special to con-. You will find it in many Latin prefixes:
- pro-: produce (verb) /prəˈdus/ vs produce (noun, fruit and vegetables) /ˈproʊdus/; progress (noun) /ˈprɑɡrɛs/ vs (verb) /prəˈɡrɛs/.
- ob-: object (noun) /ˈɑbdʒɛkt/ vs (verb) /əbˈdʒɛkt/.
- re-: works in a similar way, with an extra meaning test.
Quick summary
- Find the stress first. The spelling con-/com- tells you nothing by itself.
- Unstressed con-/com- = /kən/, /kəm/, short and weak: control, computer, connect, consider.
- Stressed con-/com- (primary or secondary) = /kɑn/, /kɑm/, the "ah" of father: contact, concert, common, conversation.
- Noun vs verb pairs switch vowels when the stress switches: CONtract /ˈkɑn-/ vs conTRACT /kən-/.
- Exceptions with /ʌ/: company, comfort, comfortable, compass.
- Pronounce a real /n/ or /m/, never just a nasal vowel.