A conditional sentence is a sentence that expresses a condition. There are different types of conditions. Some are possible or likely, others are unlikely, and others are impossible. Let’s take a look at some examples.
Is sales increase, we make more profit. This sentence is about something that is always true. This is the zero conditional.
If sales increase in the next quarter, we shall make more profit. This sentences is about something that is likely to happen in the future. It is possible that we shall make more profit. This is the first conditional.
If sales increased in the next quarter, we would make more profit. This sentence is about something that is imaginary or unlikely in the future. It is not likely that we shall make profit. This is the second conditional.
If sales had increased in the last quarter, we would have made more profit. This sentence is about the past. The sales did not increase. So, sales increase is an impossible condition. This is the third conditional.