Conditional statements are statements are sentences that express cause and effect. Kate has written a very good overview of conditional statements for this blog. As Kate says, there are four types of conditionals: the zero, first, second, and third conditionals (click here for a special grammar lesson on the third conditional). I’ll give you a brief review of these four conditionals. Then we’ll look at three modal verbs that are common in conditional statements: “could,” “should,” and “would.”
The four conditionals deal with four different kinds of cause and effect. The zero conditional deals with real cause and effect, things that really do happen. (“When the temperature drops below 0 Centigrade, water freezes.”) The first conditional deals with predictions of future cause and effect. (“If it’s sunny tomorrow, we’ll go to the beach.”) Second conditional statements mention causes and effects that are possible in theory, but are unlikely. (“If I magically grew wings, I would be able to fly.” Since it is in theory possible that magic exists, this is possible. Just not very likely at all.) The third conditional deals with causes and effects that were possible in the past, but did not actually happen. (“If Christopher Columbus had not sailed to America, someone else eventually would have.”)
Now, let’s look at the way “could,” “should,” and “would” are used in conditionals:
Could: “Could” is used to express possibility. Something that could happen is not necessarily something that must happen. Could does not express desire or opinion. It is simply used to state one or more things that are possible (even if they are unlikely) or were possible in the past (even if they didn’t happen).
First conditional example: If it rains enough tomorrow, it could flood; we should be prepared in case that happens.
Second conditional example: If I had lunch with my favorite actress, I could ask for her autograph, or I could ask her to make a movie with me.
Third conditional example: If I had known you were going to the football game yesterday, I could have gone with you, because I had the day off from work.
Should: “Should” is used to express an opinion on the best course of action. When describing cause and effect, it is also used to suggest that one cause is very likely to happen in the future, or was very likely to happen in the past.
First conditional example: If it continues to rain this hard for another hour, it should start flooding. Start preparing for the flood right now.
Third conditional examples (suggestion; event that was likely in the past): If you were going to the football game yesterday, you should have invited me to go with you. You should have known I had the day off, because I emailed you to tell you I was free.
Would: “Would” is used to describe something that is unlikely or impossible, but definitely will happen if circumstances change in a specific way. In addition, it can describe a past event that didn’t happen, but only because the circumstances were not right.
Second conditional example: If you had lunch with your favorite actress, you would ask her for her autograph and you would ask her to make a movie with you. You wouldn’t feel like you needed to choose just one of those.
Third conditional example: If I knew you had the day off yesterday, I would have asked you to join me. I wanted you to join me, but I didn’t know you were free.
There are a few things you should note. “Could,” “should,” and “would” are not used in the zero conditional. This is because the zero conditional describes things that always happen. “Could,” “should” and “would” only deal with things that may or may not happen. Additionally, “should” is not generally used in the second conditional. The second conditional deals only with things that are unlikely. If a situation is unlikely, there is little reason to give someone advice on the best course of action. Finally, “would” cannot be used in the first conditional, which deals with predictions of likely and possible future events. In conditional statements, “would” only deals with the unlikely and the impossible.
“Could,” “should,” and “would” are also used in other kinds of sentences, not just conditionals. In future posts, I will look at other uses of these three words.