Principled Reasoning


We define principled reasoning as reasoning guided by basic scientific principles and habits of mind or practices, which facilitates students’ understanding. The principles apply to multiple contexts and content areas and therefore promote learning across content areas.  Once the principles are defined, they become key to developing and using frameworks for instruction.

Two principles we have found useful are conservation of matter and energy.  These principles encompass such postulates as:

  • During chemical reactions, intramolecular bonds are broken and atoms are rearranged to form molecules of new substance as new bonds form.  No atoms are lost in the process.
  • Energy is used to break bonds, while energy is released when bonds form.
  • Objects move from positions of higher gravitational potential to lower gravitational potential. 

 Principled reasoning also involves using a coordinated set of practices which are related to the scientific principles.  In the content domains in which we work, we have found four practices to be important.

  • The practice of tracing matter includes:
    • Identifying the matter that changes, i.e. that is the inputs and outputs of a system or the reactants and products of a reaction,
    • Distinguishing matter from energy,
    • Tracing atoms, and
    • Conserving matter.
  • The practice of tracing energy includes:
    • Identifying the energy that is transformed or transferred and the forms of energy involved,
    • Describing the nature of the transformations or transfers, and
    • Conserving energy.
  • In biology, the practice of tracing information includes:
    • Identifying the form of the information (e.g. DNA base sequence, concentration of a ligand),
    • Identifying processes that transfer or transform information.
  • The practice of organizing systems and identifying scale includes:
    • Knowing the structure of the systems in which the relevant processes are taking place and
    • Selecting the appropriate level in which to reason.  In both geological and biological systems, the explanations for or mechanisms of phenomena apparent at one scale often lie at a different scale. 


Examples of using the practices to make sense of biology and geology

Tracing matter

  • In cellular respiration, tracing matter includes knowing the overall reaction (C6H12O6 + 6H2O + 6O->  6CO2 + 12H2O) and tracing individual elements through the process to see that elemental oxygen ends up in water, not carbon dioxide. Tracing matter also leads to the understanding that sugar does not turn into energy during the process of respiration.
  • In the rock cycle, tracing matter means keeping track of atoms and breaking of bonds during weathering, metamorphism, melting and recognizing the new combinations of atoms that may form during precipitation, crystallization and recrystallization.

Tracing energy

  • In both cellular respiration and photosynthesis, identifying the energy transformations from chemical potential energy in NADH/NADPH to chemical potential energy in a proton gradient to chemical potential energy in ATP helps distinguish them from chemical reactions or changes in matter and supports the understanding that atoms from NADH to not end up in ATP.

Tracing information

  • During meiosis, tracing information helps students understand why the sister chromatids of a replicated chromosome should not have different alleles. 

Organizing systems and identifying scale

  • In geology, the macroscopic view of density as something being heavy or light is explained by a molecular view of the packing of atoms or molecules. 
  • In biology, a visible plant such as a maple tree gains weight as it grows through the molecular/subcellular process of photosynthesis.

Principled reasoning in other content domains and disciplines

Our formulation of principled reasoning arises from our work in particular content domains within geology and biology.  Our work with undergraduates in other domains and disciplines suggests that lens of principled reasoning provides a useful way of looking at students’ thinking across content.  However the specifics of the suite of principles and practices that comprises principled reasoning may be specific to a discipline.