These words refer to a lack of emotional responsiveness. Impassive can pertain to a total lack of sensation or feeling: the impassive eyes of the corpse. Used in a less extreme way, it can refer to someone who remains unmoved by an emotional appeal: The judge stared down, remote and impassive , while the defence counsel pleaded for clemency. With greater suggestiveness, the word can often indicate someone who maintains a calm or unmoved exterior to conceal an emotional response: Only the faintest flicker of distaste betrayed the otherwise impassive expression with which she greeted the visiting head of state.

Apathetic and indifferent contrast sharply with this last possibility for impassive , since both point to a failure to respond. In addition, apathetic often carries a tone of criticism for a deplorable or pitiable lack of awareness, compassion or empathy: students critical of parents who had grown apathetic about glaring social evils. Sometimes, this note of criticism may be absent: slum children already sunk in apathetic despair. Where apathetic can suggest an extreme state of contumacy or listlessness, indifferent usually indicates a milder state of boredom or uninvolvement. Also, where apathetic can sometimes suggest someone dulled by adversity, indifferent can point to self-contentment as the motivating factor: The French ruling class had long been indifferent to the miseries endured by the peasants. But indifferent is less often condemnatory than apathetic ; it can be neutral or even positive: people wise enough to remain indifferent to the exhortations of demagogues – without ever growing apathetic to the threat they represented.

Insensible refers to a lack of sensation or awareness that stems either from a physiological numbness, from a steeled and determined stoicism, or from extreme preoccupation: fingers that had grown stiff and insensible with the cold; Indian braves who were taught to be insensible to the passage of time. Less approvingly, the word can refer to a callous lack of consideration for others: insensible to the needs of his wife.

Phlegmatic and stolid most often refer to a whole cast of temperament that is unemotional. Phlegmatic suggests a habitually apathetic or wishy-washy personality, lacking in forcefulness or vividness a phlegmatic dullard who was as flat as stale beer. By contrast, stolid suggests someone wooden, stiff and unbending: a coarse, stolid gaoler who could watch executions without flinching. Whereas flinching. Whereas phlegmatic can indicate someone weak, passive and yielding, even to the point of suggesting physical debilitation, stolid suggests a sturdy or unyielding rigidity of strength that is capable of surviving challenge: phlegmatic intellectuals who were no match for the stolid mass of the dictator’s adherents.