Most Indo-European languages, in addition to verb tenses (which demonstrate time), have verb moods (which indicate a state of being or reality). For instance, the most common moods in English include the following:

• The indicative (indicating a state of factuality and reality): "A cat sits on the stove." Most sentences in English are in the indicative mood. It simply states a fact of some sort, or describes what happens, or gives details about reality.
• The imperative (indicating a state of command): "Give me back my money." One marker of the imperative is that frequently the subject does not appear in the sentence, but is only implied: "(You) Give me back my money."
• The interrogative (indicating a state of questioning): "Will you leave me alone now?" One marker of the interrogative is that frequently the speaker inverts the subject-verb order by placing the helping verb first, before the subject: "Will you leave me alone?" instead of "You will leave me alone." Frequently the interrogative appears with requests for a course of action or requests for information.
• The conditional (indicating a conditional state that will cause something else to happen): "The bomb might explode if I jiggle that switch." Also, "The bomb could explode if you jiggle that switch." The conditional is marked by the words might, could, and would. Frequently, a phrase in the conditional appears closely linked to a phrase in the subjunctive (see below) preceded by a subordinate conjunction like if.

Another, rarer mood is the subjunctive mood (indicating a hypothetical state, a state contrary to reality, such as a wish, a desire, or an imaginary situation). It is harder to explain the subjunctive. Five hundred years ago, English had a highly developed subjunctive mood. However, after the fourteenth century, speakers of English used the subjunctive less frequently. Today, the mood has practically vanished; modern speakers tend to use the conditional forms of "could" and "would" to indicate statements contrary to reality. The subjunctive only survives in a few, fossilized examples, which can be confusing.

Click here to find out more about the subjunctive.