| fundamental principle(expression, reason, importance, significance) |
| fundamental reason(expression, reason, importance, significance) |
| fundamental term(expression, reason, importance, significance) |
| governing factor(expression, reason, importance, significance) |
| initial cause(expression, reason, importance, significance) |
| issue main reason(expression, reason, importance, significance) |
| key aspect(expression, reason, importance, significance) |
| key condition(expression, reason, importance, significance) |
| key element(expression, reason, importance, significance) |
| key enabler(expression, reason, importance, significance) |
| key idea(expression, reason, importance, significance) |
| key pillar(expression, reason, importance, significance) |
| key player(expression, reason, importance, significance) |
| key question(expression, reason, importance, significance) |
| key reason(expression, reason, importance, significance) |
| key role(expression, importance, significant, valuable) |
| knockout punch(expression, reason, importance, significance) |
| main cause(expression, reason, importance, significance) |
| main condition(expression, reason, importance, significance) |
| main criterion(expression, reason, importance, significance) |