The form of a root changes in some regular way.
sing
/siŋ/→ sang/sæŋ/, sink/siŋk/→/sæŋk/, stink/stiŋk/→/stæŋk/, tooth/tuθ/→ teeth/tiθ/, goose/gus/→ geese/gis/
The form of a root changes in some regular way.
sing
/siŋ/→ sang/sæŋ/, sink/siŋk/→/sæŋk/, stink/stiŋk/→/stæŋk/, tooth/tuθ/→ teeth/tiθ/, goose/gus/→ geese/gis/