The subjunctive is used: after certain impersonal expressions.
Here is a list of common impersonal expressions that introduce an aspect of uncertainty, and therefore trigger the use of the subjunctive.
| conviene que ... | it's advisable that ... |
| es aconsejable que ... | it's advisable that ... |
| es bueno que ... | it's good that ... |
| es difícil que ... | it's difficult that ... |
| es dudoso que ... | it's doubtful that ... |
| es fácil que ... | it's easy for ... |
| es fantástico que ... | it's fantastic that ... |
| es importante que ... | it's important that ... |
| es imposible que ... | it's impossible that ... |
| es improbable que ... | it's unlikely that ... |
| es incierto que ... | it's uncertain that ... |
| es increíble que ... | it's incredible that ... |
| es (una) lástima que ... | it's a shame that ... |
| es malo que ... | it's bad that ... |
| es mejor que ... | it's better that ... |
| es menester que ... | it's necessary that ... |
| es necesario que .. | it's necessary that ... |
| es posible que ... | it's possible that ... |
| es preciso que ... | it's necessary that ... |
| es preferible que ... | it's preferable that ... |
| es probable que ... | it's likely that ... |
| es raro que ... | it's rare that ... |
| es ridículo que ... | it's ridicuous that ... |
| es terrible que ... | it's terrible that ... |
| más vale que ... | it's better that ... |
| ojalá que ... | if only he would ... |
| puede ser que ... | it could be that ... |
Remember, there are also impersonal expressions that trigger the use of the indicative mood, since they introduce a quality of certainty or objectivity.
Here's a partial list of such expressions:
| es evidente que ... | it's certain that ... |
| es obvio que ... | it's obvious that ... |
| es verdad que ... | it's true that ... |
| no es dudoso que ... | it's not doubtful that ... |
| no hay duda que ... | there's no doubt that ... |