All present knowledge is built from previous knowledge. As we read, study, perform experiments, and gather perspectives, we are using other people's ideas. Building on other people's ideas, we create our own. When you put your ideas on paper, your instructors want to distinguish between the building block ideas borrowed from other people and your own newly reasoned perspectives or conclusions. You make these distinctions in a written paper by citing the sources for your building block ideas. Giving clear credit for ideas matters in the professional community as well as in school.