Tuesday, 6 March 2012

Assume vs. Presume

The dictionaries have been no friend on this. They have multiple definitions for each that are contradictory. I thought I found an opening with 'suppose' but Merriam Webster has the following definitions:
a : to lay down tentatively as a hypothesis, assumption, or proposal <suppose a fire broke out> <suppose you bring the salad>
Which conforms to assume.
(1) : to hold as an opinion : believe <they supposed they were early> (2) : to think probable or in keeping with the facts <seems reasonable to suppose that he would profit>
Which is more like presume - especially part two.

Most good bridge players know what an assumption is (see my Everything-Is-Ok-Block and Playing-Them-The-Wrong-Way-Round posts) so I will go elsewhere for examples.

Assume: Galileo disproved that heavier objects fall faster. He started by assuming that they did. He cared little for the validity of the assumption - that is why it you use assume.  He then imagined tying a heavy rock to a light rock. Following on from the assumption the light rock would retard the slow rock and they would travel at a speed somewhere between there speeds when they fell separately. However, if you have a smaller rope so that the objects were now one object then it would fall at speeds faster than the speed the speed of the heavier rock. These thoughts contradict each other and so the assumption cannot be true.

Presume: 'Dr. Livingstone, I presume' - I think the balance of probabilities is with you that the only Englishman you see for days is the one that you are looking for.


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