( ( If ( ( homogeneous matter ) ( ( can not ) ( be ( separated ( by ( physical means ) ) ) ) ) ) ) ( , ( then ( ( the matter ) ( ( is ( a ( pure substance ) ) ) . ) ) ) ) )
(ROOT (S (SBAR (IN If) (S (NP (JJ homogeneous) (NN matter)) (VP (MD can) (RB not) (VP (VB be) (VP (VBN separated) (PP (IN by) (NP (JJ physical) (NNS means)))))))) (, ,) (ADVP (RB then)) (NP (DT the) (NN matter)) (VP (VBZ is) (NP (DT a) (JJ pure) (NN substance))) (. .)))
If homogeneous matter cannot be separated by physical means, then the matter is a pure substance.
(ROOT (S (NP (NNS Elements)) (VP (VBP are) (NP (NP (JJ pure) (NNS substances)) (SBAR (WHNP (WDT that)) (S (VP (VBP make) (ADVP (RB up) (DT all) (NN matter))))))) (. .)))