Art historians are the best judges of the value of an artwork. The appropriateness of an interpretation of an artwork is relative to the general history of the period in which the interpretation is made. Interpretations of an artwork are appropriate if they originated during the period when the work was created. The colors of an artwork are relevant to an appropriate interpretation of that work.
The recent cleaning of frescoes in the Sistine Chapel has raised important asthetic issues. Art historians are now acutely aware that the colors of the works they study may differ from the works' original colors. Art historians have concluded from this that interpretations of the frescoes that seemed appropriate before the frescoes' restoration may no longer be appropriate.
Which one of the following principles, if valid, most helps to justify the art historians' reasoning?