( This ( ( ( not only ) ( ( ( ( includes ( ( both ( ( mental and ) physical ) ) fields ) ) , ) but ) ( also ( unseen ( forces ( such ( as ( ( magnetism and ) gravity ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT This)) (VP (CONJP (RB not) (JJ only)) (VP (VBZ includes) (NP (ADJP (DT both) (JJ mental) (CC and) (JJ physical)) (NNS fields))) (, ,) (CC but) (VP (ADVP (RB also)) (VBZ unseen) (NP (NP (NNS forces)) (PP (JJ such) (IN as) (NP (NN magnetism) (CC and) (NN gravity)))))) (. .)))
This not only includes both mental and physical fields, but also unseen forces such as magnetism and gravity.
(ROOT (S (NP (NNP Gravity) (CC and) (NNP magnetism)) (VP (VBP are) (NP (DT both) (JJ common) (NNS forces))) (. .)))
Gravity and magnetism are both common forces.