Variable Subjunctive Obviousness, knowledge, certainty, and hope are considered real - at least to the speaker - and therefore do not call for the subjunctive. Using these verbs and expressions in the negative or interrogative, however, indicates doubt: thus the subjunctive is required. http://www.lawlessfrench.com/grammar/variable-subjunctive/
This two-page handout contains a chart of conjugations for verbs in the subjunctive mood. There are regular and irregular verbs including spelling changing verbs. I made this for my studnets as a quick a reference/study guide.