| shaping factor(expression, reason, importance, significance) |
| top priority(expression, reason, importance, significance) |
| turning point(expression, reason, importance, significance) |
| ultimate cause(expression, reason, importance, significance) |
| underlying cause(expression, reason, importance, significance) |
| upstream cause(expression, reason, importance, significance) |
| basic cause(expression, reason, importance, significance) |
| basic condition(expression, reason, importance, significance) |
| basic premise(expression, reason, importance, significance) |
| basic prerequisite(expression, reason, importance, significance) |
| basic term(expression, reason, importance, significance) |
| bottom line(expression, reason, importance, significance) |
| break point(expression, reason, importance, significance) |
| center piece(expression, reason, importance, significance) |
| central element(expression, reason, importance, significance) |
| chief criterion(expression, reason, importance, significance) |
| chief reason(expression, reason, importance, significance) |
| controlling factor(expression, reason, importance, significance) |
| core driver(expression, reason, importance, significance) |
| critical factor(expression, reason, importance, significance) |