Per. Kun. Sen.
"Per" and "kun" represent different uses of our word "with," so care
must be taken to use the correct word.
"Per" signifies "by means of"; it denotes the "instrument" by means of
which something is done, as "Per hakilo ni hakas", By means of an axe we
chop.
"Kun" means "in company with, accompanying". "Li iros kun mi", He will
go with me.
"Sen" means "without" as "Teo sen sukero", Tea without sugar. It is used
as a prefix to denote absence of something, as "sen-utila", without
use, useless (compare with "mal", which denotes the exact opposite;
"malutila" means "harmful, noxious").