A conditional sentence is a statement which relies on one part of the sentence to be true in order for the other part to be true. Usually expressed as an "if-then" statement, a conditional sentence includes a dependent clause, or a phrase that cannot stand as a sentence, and an independent clause, or a phrase that is also a complete sentence. These two clauses are normally separated by a comma.
Although conditional sentences may come in other forms, most often they are expressed as "if-then" statements. When expressed as such, the "if" is almost always included in the dependent clause, but the "then" is more often implied. For example, the sentence, "If it snows too badly, then the school will be closed," is more often stated as, "If it snows too badly, the school will be closed." Both forms are grammatically correct, however.
There are several types of conditional sentences. They may be categorized as simply true and untrue statements or, more precisely, as facts, inferences, predictive expressions, and imaginative expressions. Facts, inferences, and predictive expressions are usually true statements, but imaginative expressions deal in the hypothetical or the impossible.
The most straight-forward of all conditional sentences is likely the fact. Facts simply express a cause and effect situation that is always the same. For example, "If water reaches a temperature below 32°F; (0°C;), it turns to ice." Since 32°F; (0°C;) is the freezing point of water, this statement is factual.
Alternatively, a conditional sentence that expresses an assumed effect to a given cause is normally an inference. Statements that assume if one person can accomplish something another can, such as, "If I can do it, you can," are inferences. Also, sentences such as, "If it's a holiday, we don't need to go to work," fall under this category.
Predictive expressions usually indicate plans or desired courses of action. They depend on the truth of the "if" statement to be accurate, but do not assume the "if" statement is accurate. Often, these expressions describe possible future events. For example, the sentence, "If I save enough money, I will go to on vacation," depends on the "if" clause to be true in order for the "then" clause to also be true. Predictive expressions usually employ the future tense in the "then" part of the statement.
Imaginative expressions may be hypothetical or impossible. A hypothetical conditional sentence is similar to a predictive conditional sentence but states something that is possible but unlikely, rather than likely but not factual. For example: "If I saved enough money, I would go on vacation." The hypothetical uses the past tense in the "if" portion of the sentence and "would" in the "then" portion.
Similarly, impossible situations also fall under the imaginative category. When an impossible situation is expressed, usually the past perfect is used in both clauses and the word "would" is used in the "then" statement. Impossible situations can often be categorized as past unrealized plans. For example: "If I had saved enough money, I would have gone on vacation."