What is a good explanation?

An explanation can be considered a statement about what is there, what it does, how it works, and why.  But when we set out to provide explanations for the phenomena of our physical reality, how can we determine if we have arrived at a good explanation rather than a bad one?   A good explanation will be hard to vary, while still accounting for what it is meant to account for. 

For example, consider our understanding of the regularity of seasons on Earth.  For millennia, elaborate myths involving gods and their activities have been often conjectured as reasons for earthly seasons but these are poor explanations because they are easy to vary.  If you were to dispute these explanations (for whatever reason) new gods with different activities could be easily substituted, and there is no way to judge between such easy to vary explanations.  Their ability to explain what is really happening is very limited.  

An explanatory theory for seasons that is based on the theory that the Earth is round, tilted, rotating, and revolves around the sun every 365 days, is a much better explanation, as it is a theory that is difficult to vary.  As a good explanation it gives us a much better understanding of our reality.

 

The best explanation will also meet all the criticisms we have for it at the moment and won't have any good rivals.  

Many good explanations also have reach, which is the ability to solve problems beyond those that they were created for.   In the example above, this theory also explains how seasonal changes can take effect on other planets, as well as many other related phenomena.  The best explanations have universal reach.

​

Once we have a really good explanation for something, it likely contains knowledge that was hard to come by, and it will likely explain more than just what it set out to explain.  After that it will be difficult to go back to easy explanations, such as the gods causing the seasons.  They will be recognized for their inadequacy.

​