In the English language, a verb mood indicates the action or condition in which the verb is conceived or intended. The most frequently used verb mood in English is the indicative mood, which describes knowledge or beliefs. The subjunctive mood appears in two types of sentences: those in which either unlikely conditions are presented or others where desires/requests are expressed in using the word "that."
Hypothetical expressions are always formed using the subjunctive mood. These expressions indicate unlikely or unreal conditions. Some examples of hypothetical conjunctions used to express hypothetical situations are: if, whether .. or not, on the condition that .., unless, without etc. It is important to remember that if there is only one subject for the two subordinate clauses, conjunctions may be replaced by prepositions, in which case there is no subjunctive conjunction.
Although the if/then construction is often used to express hypothetical situations, it is important to know that it can be used to express other mood and tense patterns as well. If/then clauses that are not hypothetical/subjunctive can express: no uncertainty; some uncertainty; in the future without uncertainty; an unlikely case in the future; or a case that never happened in the past.
Aside from the hypothetical form, subordinate conjunctions are used in subjective commands. The command form is used to express a requirement or statement of purpose. In command sentences, the conjunction "that" follows the verb of first clause to join the ideas from both the first and second clauses.