According to Celce-Murcia and Larsen-Freeman (1999), conditionals present three kinds of semantic relationships:

a. Factual Conditional Relationships
b. Future (Predictive) Conditional Relationships
c. Imaginative Conditional Relationships

Yule (2000) has a similar classification for conditionals. In addition, he states that the meaning of conditionals can be considered as answers to the following questions:

• What happens if...?
• What will happen if...?
• What would happen if...?
• What would have happened if...?

This type of conditionals has the following sub-divisions:

Generic Factual Conditionals

These are used to refer to true relationships that remain unchanged. These sentences usually contain the present tense in both clauses and are present in scientific writing. Examples:

• If the wind blows, seeds are spread.
• If sand is mixed with water, the sand goes to the bottom.

Habitual Factual Conditionals

These also express a true relationship. The relationship here is based on a habit instead of scientific facts. The present tense can be used here as well as the past tense and also has the same tense in both clauses. Examples:

• If it rained heavily, we hid under the tent.
• If I get up last, I make the bed.
• If they went out, they took all the dogs with them.

Implicit Inference Conditionals

The relationships expressed here are time-bound as expressed by Celce-Murcia and Larsen-Freeman (1999), this type of conditional makes use of different tenses and some modals are included. Examples:

• If young people are still not aware of the dangers of smoking, all the campaigns have failed.
• If you can work with children, you can work with any audience.

Explicit Inference Conditionals

This type of conditional is used to express specific events, but unless the precedent, this conditional makes the inference explicit by using a modal. These sentences may refer to past or present events. Examples:

• If you were at the library this afternoon you must have seen me there.
• If someone calls me, wake me up. It must be my boss.

b. Future (Predictive) Conditional Relationships

This variety of conditional is utilized to communicate plans or talk about unforeseen events. In the structure of this conditional the subordinate clause is in present and the main clause is in future (will). Examples:

• He will give us a ride if we meet him at the parking lot.
• If it rains we won't go to the game.
• If we go there by car, it will take about 6 hours.

The use of the modal "will" here expresses a strong condition or a strong outcome. However, this certainty can be weakened if we use other modals:

c. Imaginative Conditional Relationships

It can be divided into two categories:

Hypothetical Conditionals

According to Yule (2000), hypothetical conditionals are used to discuss the results of choosing an alternative when different options are offered. Examples:

• If we go by plane we would save a lot of time.
• On the other hand if we go there by car we would save a lot of money.

Counterfactual Conditionals

The precedent imaginative conditional expresses that something is very unlikely to happen. However, it might happen.

• If I were born again, I would do things differently.

It is obvious that the state of "being born" cannot be changed under any circumstance. The counterfactuals have different meanings, which will be explained in the next section.