These words all refer to a highly developed mental ability to see or understand what is not obvious. Acumen has to do with keenness of intellect, and implies an uncommon quickness and discrimination of mind. It requires acumen to solve an intricate problem in human relationships, or to emerge unscathed from a venture into the stock market.

Insight and perception mean the power to recognize the hidden springs of behaviour or the true nature or cause of a situation or condition: A psychiatrist’s insight into human behaviour may uncover the underlying cause of a boy’s delinquency; a doctor’s perception may recognize a patient’s complaints as symptoms of a psychic disorder. Perception in its basic sense applies to anything recognized or understood by the senses, and in its extended sense to anything recognized or understood by the mind, thus suggesting a likeness between mind and the senses. Perception therefore suggests a view of the mind as a keenly receptive but none the less passive instrument, sensitive to very slight stimuli. Insight, on the other hand, is consistent with a view of the mind as an active agent, seeking and sifting ideas and probabilities as well as the evidence of sensations. In most contexts insight implies a more profound use of intellect and wisdom than does perception ; insight suggests a knowledge of the inner character or essence of a thing, whereas perception relies primarily on the sharpness or acuity of one’s senses.

Acuity means sharpness or keenness, and is applied exclusively to perception : visual acuity ; The intelligence test was used as a basis for judging his mental acuity .