Some words are made up of a root and a suffix:
dangerous = root –> danger + ous –< suffix
commercial = root –>
commerc(e)
+ al –< suffix
In some words with suffixes, the stress stays on the same syllable as in the root. Compare:
‘danger and: ‘dangerous
In other words, the suffix changes the stressed syllable. Compare:
‘commerce and: com‘mercial
Suffixes which don’t usually change the stress pattern in the root word include (however they maybe some exceptions.) -able, -age, -al, -er, -ful, -less, -ness, -ous and -fy. For example:
comfort – ‘comfortable
per
‘cent – per’
centage
e
‘lectric – e
‘lectrical
‘amplify –
‘amplifier
re
‘gret – re
‘gretful
re
‘gard – re
‘gardless
‘foolish –
‘foolishness
di
‘saster – di
‘sastrous
‘beauty –
‘beautify
(However they maybe some exceptions.) Exceptions with -able and -al include:
ad‘mire – ‘admirable
pre
‘fer –
‘preferable
‘medicine – me
‘dicinal
‘agriculture – agri
‘cultural