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Wordpecking: Assume vs. Presume

CanOxEvery once in a while, when we’re far away from books and my phone is low on power or signal (or both), my hubs will throw a language question at me. Last night the question was “what’s the difference between assume and presume?”

A different kind of person might just say, “you’ve got a phone; ask Grammar Girl“. But I rather enjoy wordpecking — my term for testing my understanding of the language against acknowledged sources — so in I dove.

Both assume and presume have a variety of meanings, but he was asking about the “drawing conclusions” sense of the words. A lot of people use them interchangeably or without really knowing why they use one or the other in a given situation. After a minute’s thought, I came up with “assume means to draw a conclusion without proof; presume means to draw a conclusion without proof but based on existing knowledge.”

How’s that for a fine distinction? We agreed that the difference between the two is a matter of confidence or certainty. When you presume something is true, you are more confident about its probability than when you merely assume it is true.

The second part of wordpecking is to look things up in acknowledged authorities. To the dictionaries!

Merriam-Webster’s definitions seem to be the reverse of my thinking. Their first definition of assume is “to think that something is true or probably true without knowing that it is true” [emphasis mine]. Their first definition of presume is “to think that (something) is true without knowing that it is true.”

Thus, the probability aspect is part of assume at Merriam-Webster. At other internet sources, however, the implied confidence, certainty, or probability is ascribed to presume. Vocabulary.com, Oxforddictionaries.com, and Grammarly.com all agree on this point.

My hard-copy Canadian Oxford Dictionary‘s first definition of assume is “(often foll. by that + clause) take or accept as being true, without proof, for the purpose of argument or action.” Presume‘s first definition is “(often foll. by that + clause) suppose to be true; take for granted.”

The addition of “for the purpose of argument or action” is an interesting distinction for assume. And even though CanOx makes no mention of probability or certainty in its definition of presume, it’s certainly implied by “take for granted”.

Sorry, Merriam-Webster, you’re outvoted on this one. Oh, and interesting note about Grammar Girl: to my surprise, she doesn’t have an entry for this particular matter of usage.

I assumed Merriam-Webster’s definitions would accord with mine, and I presumed that Grammar Girl would have an entry citing chapter and verse on the matter. I was mistaken on both counts.

Well, that was fun! Got any other words you’d like me to wordpeck? Leave ’em in the comments. That’ll be a fun way to christen my new reference books.

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