A grammatical mood is a form of a verb that expresses mode of action. In some languages, the conditional mood is used to describe circumstances that might or might not happen. English does not have a fully developed conditional mood, but expresses the same idea by using the modal verb "would."
Conditional sentences are those that contain at least one statement that is untrue, uncertain or dependent on another event. Often they have two clauses, an "if" clause known as the protasis, and a "then" clause called the apodosis. For example, in the sentence, "If you were kind to me, then I would be your friend," the first clause is the protasis, and the second is the apodosis. The first clause is in the subjunctive mood — "were kind" — to show that it is contrary to fact. Also indicating a statement contrary to fact, the apodosis uses the modal phrase, "would be."
Some grammarians say that "would be" is in the conditional mood in English. Others, however, claim that since "would" is not conjugated, it is simply part of the indicative mood. Regardless of its exact grammatical classification, however, the word "would" conveys the same sense as the conditional mood in other languages. In French, je serais, which is conjugated in the conditional mood, is translated "I would be" and used in the apodosis of a conditional statement to indicate a statement contrary to fact.
Unlike the English verb "would," however, conditional verbs in most languages cannot be used in the protasis. For instance, in English one could say, "If you would be on time, then you could get all your work done." Most romance languages, however, would put the protasis of this sentence either in the indicative or the subjunctive mood.
A few languages use the conditional mood as a polite form of expression, rather than to describe true conditional statements. For example, the French je voudrais, "I would like," might be used when ordering food in a restaurant. The form of this phrase is the same as the one used in conditional sentences, even though the meaning is different.