1. Patterns. Observed patterns of forms and events guide organization and classification, and they prompt questions about relationships and the factors that influence them.
2. Cause and effect: Mechanism and explanation. A major activity of science is investigating and explaining causal relationships.
3. Scale, proportion, and quantity. In considering phenomena, it is critical to recognize what is relevant at different measures of size, time, and energy.
4. Systems and system models. Defining the system under study provides tools for understanding and testing ideas that are applicable throughout science and engineering.