then vs and so

then is a noun but and so is not a noun.

Word	Noun	Adjective	Verb	Adverb
then	Yes	Yes	No	Yes
and so	No	No	No	Yes

As adverbs, then and and so are synonyms defined as:

then and and so: subsequently or soon afterward (often used as sentence connectors)

Other synonyms of then include so.

then (noun)	and so (noun)
that time; that moment

then (adjective)	and so (adjective)
at a specific prior time

then (adverb)	and so (adverb)
subsequently or soon afterward (often used as sentence connectors)	subsequently or soon afterward (often used as sentence connectors)
at that time
in that case or as a consequence