 Reduction may be understood in multiple ways depending on what it is that is being reduced (see the entry on  scientific reduction).  Theory reduction pertains to whether or not theories from one scientific field can be reduced to theories from another scientific field. In contrast, explanatory reduction (often united with methodological reduction) pertains to whether or not explanations that come from lower levels (often united with methodologies that investigate those lower levels) are better than explanations that come from higher levels. Philosophical attention to molecular biology has contributed to debates about both of these senses of reduction (see the entry on  reductionism in biology).