Tip #34: Always compare to similarities and with differences

I’ve said it before.  And I’ll say it again because it never gets old.  Many of the difficulties we encounter in writing stem from failing to separate written English from spoken English.  They are two different animals.

Here’s yet another common manifestation of that reality.  Note the sample text in the image at right.  Let's take a look at the first sentence in the image.

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The material selection report compares Type 410 to Type 416 for use in exhaust manifolds.

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Type 410 and Type 416 are both martensitic stainless steels.  Both materials have high strength and can be hardened by heat treatment.  The sample sentence uses these two materials as the objects of a comparison.  Because of the similarity in the objects of the comparison, the preposition to is used in the sample sentence.

But one important difference exists between Types 410 and 416 stainless steel.  Type 410 is a general martensitic stainless steel; other martensitic stainless steels are just modifications of Type 410.  Type 416 is no exception; it contains extra phosphorus and sulfur to improve machinability.  So if the author wanted to focus on the difference, he or she would use the preposition with.

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The material selection report compares Type 410 with Type 416 for use in exhaust manifolds.

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Many English speakers make no distinction between compare to and compare with.  Yet that’s not really the case.  Compare to is used to highlight similarities, whereas compare with is used to highlight differences.  

That’s a very significant distinction.  And respecting that distinction makes for clearer writing, which always makes for better writing.