‘sober’ is an adjective, ‘up’ is an adverb/particle, but ‘sober up’ is a verb.
‘It is sobering to realize that ..’ is OK. So, ‘sober’ is a verb with at least some inflections. I can’t think of any other similar examples. ‘man up’ is noun + adverb/particle. ‘slow’ as in ‘slow down’ is both an adjective and verb.
Bound morpheme ‘-en’ is more productive.
‘sicken’
‘lessen’, but not ‘more-en’.
‘weaken’, but ‘strengthen’ not ‘strongen’.
‘shorten’, but ‘lengthen’ not ‘longen’.
‘lower’, but no ‘lowen’, and ‘heighten’ not ‘highen’.
‘widen’, but ‘narrow’ is already a verb.
‘freshen’, but what is the opposite of ‘fresh’?
‘quicken’ is in common use? No ‘slowen’.
‘enlarge’, but ‘largen’ and ‘enlargen’ are words?
‘-ize’ is probably even more productive.
A search of /usr/share/dict/words will find examples of both.
Me atBack to WobblyEnglish