Is it farther or further?
mid-15c., "pertaining to a political subject" (now obsolete), from Late Latin subjectivus, from subjectus (see subject (n.)). Meaning "existing in the mind" (mind="the thinking subject") is from 1707; thus, "personal idiosyncratic" (1767). Related: Subjectively.
subjective sub·jec·tive (səb-jěk'tĭv)
Of, relating to, or designating a symptom or condition perceived by the patient and not by the examiner.
Existing only in the mind; illusory.