In English, the vowel sound in a syllable often changes depending on if the syllable is stressed or unstressed.  A useful starting point to learn about this is with a sound that sounds like ‘uh’ and is represented by two symbols in the IPA. It is the most common sound in English. It is ubiquitous because in most cases the vowel that is the syllable core changes to this sound when the syllable is unstressed. In unstressed syllables, the sound is called a schwa and is represented by an upside-down ‘e’ [ə].  

One place this happens frequently is the “-ed” suffix following a consonant such as ‘t,’ ‘d,’ or ‘g.’  So we pronounce “waited” [weɪtəd] (WAY-tuhd), the short “uh” separates the ‘t’ sound from the ‘d’ sound. The stress is in the ; [eɪ] (ay) so the ‘e’ is unstressed and pronounced [ə] (uh).

The word “the” [ðə] (thuh) is not stressed, because it is a function word (next section).

The ‘uh’ sound can be a vowel in stressed syllables too. In that case, it is represented by the symbol [ʌ] which is called, “tuned v,” “caret,” “circumflex” and “wedge.” I am calling it ‘wedge” here. Wedge [ʌ] is the symbol for the ‘uh’ sound in words like “but,” “cut,” “shut” which are almost always stressed

This applies in sentences too. If a syllable is unstressed in a sentence, the vowel is usually reduced to a schwa. Function words are not stressed, so the vowels in function words are usually reduced to schwa, as in “I’m going to the store” [aɪm ˈɡoʊɪŋ tə ðə ˈstɔr] (IEm gOH-ing tuh thuh stOR). This is discussed in the next section.

Any English letter that represents a vowel, ‘a,’ ‘e,’ ‘i,’ ‘o,’ or ‘u’ can be reduced to schwa [ə] (or another more central vowel) in an unstressed syllable. Occasionally (more often in some dialects than others) [i] is reduced to [ɪ]. These reductions make English spelling difficult because you can’t sound out the spelling of the word.

What follows are lists of words of one, two, three, and four syllables in four formats. First is the word itself (a “gloss”), next is the word with the stressed syllable in capital letters, then the word in using phonetic spelling with the stressed vowel in capital letters, and final the IPA (International Phonetic Alphabet) spelling. In the IPA spelling, the stressed syllable is proceeded by a stress marker (ˈ).

The lists have phonetic spelling and the IPA spelling of the way that the word is said. In most cases, one of the vowels changes. There are some syllables that are never stressed and even when the word is pronounced slowly you do not make the full vowel sounds.  For instance, the ending ‘-ed’ [əd] for the past tense is never stressed, but it can be stressed in “bed” [bɛd]

Be sure and notice that not every unstressed vowel is reduced to schwa (ə), in some cases, [i] is reduced to [ɪ] which lowers the [i] and makes it more central (see the vowel chart).

Vowel Change in Two-Syllable Words

	Word	Stress	Phonetic Spelling	IPA
1.	“again”	a-GAIN	uh-gEn	əˈɡɛn
2.	“avoid”	a-VOID	uh-vOId	əˈvɔɪd
3.	“behaved”	be-HAVED	bi-hAYvd	bɪˈheɪvd
4.	‘billion”	BILL-ion	bIl-yuhn	ˈbɪljən
5.	“brilliant”	BRILL-iant	BɹIl-yuhnt	ˈbɹɪljənt
6.	“buildings”	BUILD-ings	bIl-dingz	ˈbɪldɪŋz
7.	“collapsed”	co-LLAPSED	kuh-lApst	kəˈlæpst
8.	“discuss”	DI-scuss	di-skUHs	dɪˈskʌs
9.	“hundred”	HUN-dred	hUHn-druhd	ˈhʌndɹəd
10.	“kitten”	KITT-en	kIt-n	ˈkʰɪʔn̩
11.	“mountain”	MOUNT-ain	mOUnt-n	ˈmaʊntn̩
12.	“playful”	PLAY-ful	plAy-fuhl	ˈpleɪfəɫ
13.	“police”	pol-ICE	puh-lEEs	pəˈlis

Vowel Changes in Three-Syllable Words

	Word	Stress	Phonetic Spelling	IPA
1.	“adequate”	AD-e-quate	Ad-uh-kwuht	ˈæɾəkwət
2.	“attention”	a-TTEN-tion	uh-tEn-shuhn	əˈtʰɛnʃən
3.	“attractive”	a-TRAC-tive	uh-trAk-tiv	əˈtɹæktɪv
4.	“complement”	COM-ple-ment	kAHm-pluh-muhnt	ˈkʰɑmpləmənt
5.	“conference”	CON-fer-ence	kAHn-fuhr-ruhns	ˈkʰɑnfɚɹəns
6.	“connection”	co-NNEC-tion	kuh-nEk-shuhn	kəˈnɛkʃən
7.	“customary”	CUS-to-mary	kUHs-tuh-mair-ee	ˈkʰʌstəmɛri
8.	“difficult”	DIF-i-cult	dIf-i-kuhlt	ˈdəfɪkəɫt
9.	“dilemma”	di-LEMM-a	duh-lEm-uh	dəˈlɛmə
10.	“documents”	DOC-u-ments	dAHk-yuh-muhnts	ˈdɑkjəmənts
11.	“easily”	EA-si-ly	EE-zuh-lee	ˈizəli
12.	“exhaustion”	ex-HAUS-tion	ig-zAHs-chuhn	ɪɡˈzɑstʃən
13.	“horizon”	ho-RIZ-on	huhr-rIEz-n	hɚˈɹaɪzn̩
14.	“numerous”	NU-mer-ous	nOO-muhr-ruhs	ˈnumɚɹəs
15.	“persistent”	per-SIS-tent	puhr-sIs-tuhnt	pɚˈsɪstənt
16.	“photograph”	PHO-to-graph	fOH-tuh-graf	ˈfoʊɾəɡɹæf
17.	“substitute”	SUB-sti-tute	sUHb-stuh-toot	ˈsʌbstəˌtut
18.	“terrible”	TERR-i-ble	tAIR-uh-buhl	ˈtʰɛrəbəɫ
19.	“typical”	TYP-i-kuhl	tIp-uh-kuhl	ˈtʰɪpəkəɫ

Vowel Changes in Four-Syllable Words

	Word	Stress	Phonetic Spelling	IPA
1	“copulation”	cop-u-LA-tion	kahp-yuh-lAY-shuhn	kɑpjəˈleɪʃən
2	“dictionary”	dic-TION-ar-y	dIk-shuh-nair-ee	ˈdɪkʃən'ɛrɪ
3	“directory”	dir-EC-tor-y	duhr-rEk-tuhr-ree	dɚˈɹɛktɚɹi
4	“disestablish”	dis-e-STAB-lish	dis-uh-stAb-lish	ˌdɪsəˈstæblɪʃ
5	“execution”	exe-c-U-tion	ek-si-kyOO-shuhn	ˌɛksɪˈkjuʃən
6	“insoluble”	in-SOL-u-ble	in-sAHl-yuh-buhl	ɪnˈsɑljəbəl
7	“mandatory”	MAN-da-tor-y	mAn-duh-tor-ee	ˈmændəˌtɔri
8	“obligation”	ob-li-GA-tion	ahb-luh-gAY-shuhn	ˌɑbləˈɡeɪʃn̩
9	“persecution”	per-se-CU-tion	puhr-si-kyOO-shuhn	ˌpɝsɪˈkjuʃən
10	“population”	pop-u-LA-tion	pahp-yuh-lAY-shuhn	ˌpɑpjəˈleɪʃən
11	“supposedly”	su-PPO-sed-ly	suh-pOH-zuhd-lee	səˈpoʊzədlɪ
12	“television”	TEL-e-vis-ion	tEl-uh-vizh-uhn	ˈtɛləˌvɪʒən
13	“termination”	ter-mi-NA-tion	tuhr-muh-nAY-shuhn	ˌtɝməˈneɪʃən
14	“undoubtedly”	un-DOUB-ted-ly	uhn-dOU-tuhd-lee	ˌʌnˈdaʊtədlɪ

Words Where Stress Changes the Meaning

	Word		Stress	Phonetic Spelling	IPA	POS	Meaning
1	“address”	a.	AD-dress	A-dres	æd`ɹɛs	(N)	A symbolic representation of a location.
		b.	ad-DRESS	uh-drEs	əˈdɹɛs	(V)	Write directions for delivery; direct your focus to.
2	“convert”	a.	CON-vert	kAHn-vuhrt	ˈkɑn,vɝt	(N)	a person who has been persuaded to change their religious faith or other beliefs.
		b.	con-VERT	kuhn-vUHRt	kənˈvɝt	(V)	Cause to change in form, character, or function.
3	“decrease”	a.	DE-crease	dEE-krees	ˈdi,kɹis	(N)	Something that has been reduced.
		b.	de-CREASE	di-krEEs	dɪ`kɹis	(V)	Cause the reduction of something.
4	“invalid”	a.	IN-val-id	in-vuh-luhd	ɪnvələd	(N)	A person made weak or disabled by illness or injury.
		b.	in-VAL-id	in-vAL-uhd	ɪn`væləd	(A)	The action of object is not valid.
5	“recall”	a.	RE-call	rEE-kahl	`ɹi,kɑl	(N)	An act or instance of officially recalling someone or something
		b.	re-CALL	ruh-kAHl	ɹə`kɑl	(V)	To remember something.
6	“refuse”	a.	RE-fuse	rEE-fyoos	ˈɹɛ,fyus	(N)	Waste or garbage left over from an event.
		b.	re-FUSE	ri-fyOOz	ɹɪ`fjuz	(V)	To express oneself as unwilling to accept
7	“subject”	a.	SUB-ject	sUHb-jikt	sʌbd͡ʒɪkt	(N)	A person or thing that is being discussed, described, or dealt with.
		b.	sub-JECT	suhb-jEkt	səb`d͡ʒɛkt	(V)	Cause or force to undergo (a particular experience of form of treatment).
8	"record"	a.	RE-cord	REE-kord	ɹɛ'kɚd	(N)	A vinyl disk with recorded sound.
		b.	re-CORD	ruh-kOrd	ɹɪ'kʰɔrd	(V)	The act of recording sound.