All these words suggest a tendency to persist in an opinion, belief, decision or course of action, generally with more force than reason. A person may be stubborn by disposition, showing this quality in most of his behaviour and in most situations, but may be obstinate in a particular instance: Dick had always been a very stubborn boy, but was particularly obstinate in his dislike of homework. Pigheaded usually suggests obstinate stupidity: His pigheaded refusal to accept facts makes discussion impossible. Adamant and inflexible imply a hard and unyielding attitude that may be the result of a strongly felt or carefully thought out conviction regarding some important matter: The ambassador was adamant in his insistence that all the prisoners be released from the concentration camp. Inflexible suggests more of an unwillingness to change one’s mind and usually carries notions of the foolish firmness implied by the more pejorative pigheaded : He remained inflexible even when the wisdom of changing his mind must have been obvious. A similar attitude, but carrying the idea of harshness and a lack of felling, is implied by obdurate : The foreman was obdurate in holding to rigid production schedules. Both adamant and obdurate can point approvingly to principled refusal to compromise, unlike these other words with their implications of arbitrary egocentricity.

Pertinacious , though not necessarily deprecatory, usually suggests a kind of perseverance in a course of action that can be annoying or seem unreasonable to others: The lawyer’s pertinacious harping on the same point made the witness very nervous under cross-examination. Headstrong indicates a strong-willed self-direction and an impatience with restraint. A headstrong person cannot be held back by advice or argument and may be reckless or hotheaded in his actions: a headstrong impetuous youth, rushing into things without forethought; His headstrong attempt to seize control of the party was political suicide.