Topic 2: Introduction to Nuclear Energy – Step 16

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English Idiom

“Rule of Thumb”


In the next video, Ferenc uses the term “rule of thumb.” What does this mean?

Source: Rolls off the Tongue

Rule of Thumb: A means of estimation made according to a rough and ready practical rule, not based on science or exact measurement.  A general, not exact, rule.

The phrase itself has been in circulation since the 1600s. In 1692, it appeared in print in Sir William Hope’s training manual for aspiring swordsmen, The Compleat Fencing-master:

“What he doth, he doth by rule of Thumb, and not by Art.”

The origin of the phrase remains unknown. It is likely that it refers to one of the numerous ways that thumbs have been used to estimate things – judging the alignment or distance of an object by holding the thumb in one’s eye-line, the temperature of brews of beer, measurement of an inch from the joint to the nail to the tip, or across the thumb, etc. The phrase joins the whole nine yards as one that probably derives from some form of measurement but which is unlikely ever to be definitively pinned down. The Germans have a similar phrase to indicate a rough approximation – ‘pi mal daumen’ which translates as ‘pi [3.14…] times thumb’.

Modern-day example:

“When making friends on Facebook, asking in advance is a good rule of thumb to avoid the discomfort of having a friend ignore your request.”


The Phrase Finder

Rolls of the Tongue