A.T. Robertson Commentary Hebrews 5:14

"But solid food is for fullgrown men, [even] those who by reason of use have their senses exercised to discern good and evil." — Hebrews 5:14 (ASV)

For full-grown men (τελειων). Predicate genitive. The word is for adults, relative perfection (τελειο) in contrast with babes as in 1 Corinthians 2:6; 3:1; 13:11; Php 3:15; Ephesians 4:4, not absolute perfection (Matthew 5:48).

Their senses (τα αισθητηρια). The organs of perception (Stoic term for sense organs) from αισθανομα (Luke 9:45), in Plato, Galen, Hippocrates, here only in N.T.

Exercised (γεγυμνασμενα). Perfect passive participle of γυμναζω, to exercise (naked, γυμνος). Galen uses αισθητηρια γεγυμνασμενα together after εχω as we have here. For this predicate use of the participle with εχω see Lu 13:6; 14:19f. "By reason of use" one gains such skill.

To discern (προς διακρισιν). "For deciding between" (from διακρινω), old word with ablative καλου τε κα κακου (between good and evil). See 1 Corinthians 12:1; Romans 14:1.