Understanding the scientific reasoning behind a laboratory procedure is critical to the student's understanding of the scientific process and has become increasingly important. in the introductory project-based laboratory curriculum at Brandeis University, we ask our students to write true scientific purposes for each laboratory in place of learning objectives. With discussion, feedback, and practice, we find that this simple exercise increases our students' understanding of the material and their ability to write abstracts and solidifies the underlying connections between multiweek procedures.