They are called supporting ideas because they "support" the topic sentence. Our TOEFL essay's supporting ideas all come after the topic sentences. They support the topic sentence by telling the reader why we believe the topic sentence is true.Supporting ideas can be almost anything. Once you have decided on your topic and your main controlling idea, you need to choose the two, three, or four supporting points about the topic. The topic is what the paragraph or essay is about, the supporting points are the most important things you have to say about your topic.