Full Idea
There are many forms of reasoning - extrapolation, interpolation, and other arguments from analogy - that are useful but deductively invalid.
Gist of Idea
Many forms of reasoning, such as extrapolation and analogy, are useful but deductively invalid
Source
Stephen Mumford (Laws in Nature [2004], 04.4)
Book Reference
Mumford,Stephen: 'Laws in Nature' [Routledge 2006], p.62
A Reaction
[He cites Molnar for this]