These alone could have valuable uses.
( These ( alone ( ( could ( have ( valuable uses ) ) ) . ) ) )
(ROOT (S (NP (DT These)) (ADVP (RB alone)) (VP (MD could) (VP (VB have) (NP (JJ valuable) (NNS uses)))) (. .)))
They aren't valueable. 
( They ( ( ( are n't ) valueable ) . ) )
(ROOT (S (NP (PRP They)) (VP (VBP are) (RB n't) (ADJP (JJ valueable))) (. .)))