| natural(spontaneous, voluntary) |
| no strings attached(expression, idiom, open, free, voluntary) |
| noncompulsory(open, free, voluntary, elective) |
| nonobligatory(open, free, voluntary, elective) |
| not required(expression, open, free, voluntary, elective) |
| obdurate(deliberate, determined, intentional) |
| obstinate(deliberate, determined, intentional) |
| open(free, voluntary, elective) |
| persistent(deliberate, determined, intentional) |
| pertinacious(deliberate, determined, intentional) |
| perverse(deliberate, determined, intentional) |
| pigheaded(deliberate, determined, intentional) |
| possible(voluntary, elective) |
| purposeful(deliberate, determined, intentional) |
| purposive(deliberate, determined, intentional) |
| refractory(deliberate, determined, intentional) |
| resolved(deliberate, determined, intentional) |
| self-willed(deliberate, determined, intentional) |
| stiff-necked(deliberate, determined, intentional) |
| studied(deliberate, determined, intentional) |