canto talk about possibility and certainty in English. A speculation is when you use the evidence in a situation to make an opinion about it. To form your opinion, you ask yourself, “What has happened or not happened based on what I know or see?” You don’t know for sure that your opinion is true, but you can make an informed guess. For example, imagine your friend told you she would call at 6 p.m., but she did not. What could you speculate or deduce? She MIGHT have forgotten. She COULD have been too busy. Something urgent MAY have come up. In this advanced English grammar lesson, we will discuss all the grammar you need to make a speculation or deduction in English.