go upstream, retrace the past
遡 centers on moving against a current to reach an earlier point: going upstream or tracing events back through time.
遡 combines the movement radical 辶 with 朔, which likely contributes the sound and the idea of going back to the beginning, as in the first day of the lunar month.
The movement radical 辶 wraps around 朔, which suggests the start of a month. Picture walking backward along a river to its source, retracing the path to the beginning.
For ソ, imagine going upstream in a small boat, rowing against the current: the sound of the oars is 'so, so' as you retrace the river's path.
to go upstream; to go up (a river)
retroactivity; retroaction; being retroactive (to)
going upstream; sailing against the current
non-retroactivity
going upstream; swimming upstream
retrospective bibliography
retroactive law; retrospective law
retroactive
redemption; recourse
right of recourse; right for redemption
anadromous fish (fish that migrates upstream, e.g. salmon)
going to the source; tracing to the origin