Can someone help me dissect this sartre quote?

If
 one 
begins
...
by 
taking
 knowledge as 
a 
given,
 without
 being
 concerned 
to 
establish 
a 
basis 
for 
its
being, 
and
 if 
one 
then 
affirms
 that 
esse
est
 percipi,
 the 
totality 
“perceived‐perception” 
lacks 
the 
support
of
 a 
solid 
being
 and 
so
 falls 
away
 in 
nothingness.