In the spirit of &quot;reading philosophy backwards&quot; [1]:<p>Peirce is spot-on about &quot;force&quot;—in the 138 years since this essay, there has been no progress on the question of &quot;what is force?&quot;, but huge progress on the question &quot;what mathematical relations do forces satisfy?&quot;. Peirce must be writing in opposition to someone&#x27;s unsuccessful attempts to describe or define the nature of &quot;force&quot;. (But who was that?)<p>I&#x27;m less convinced about &quot;hardness&quot;. Today we&#x27;d be happy to describe the hardness of an object even if it never came into contact with anything, whereas Peirce writes, &quot;There is absolutely no difference between a hard thing and a soft thing so long as they are not brought to the test.&quot; But maybe that&#x27;s because we conceptualize &quot;hardness&quot; differently from Peirce? That is, now we think of hardness as an intrinsic property that can be deduced from the structure and chemical composition of an object and measured on something like the Brinell scale (1900), whereas Peirce is thinking about it as a partial order based on something like the Mohs scale (1812)?<p>[1] <a href="http:&#x2F;&#x2F;slatestarcodex.com&#x2F;2013&#x2F;04&#x2F;11&#x2F;read-history-of-philosophy-backwards&#x2F;" rel="nofollow">http:&#x2F;&#x2F;slatestarcodex.com&#x2F;2013&#x2F;04&#x2F;11&#x2F;read-history-of-philoso...</a>