Impervious and Impenetrable
The synonyms impervious and impenetrable have similar meanings, but, depending on context, one is preferable to the other.
The words are used both literally and figuratively. Here are their literal meanings:
impervious: Through which there is no way; not affording passage (to); not to be passed through or penetrated; impenetrable, impermeable, impassable.
impenetrable: That cannot be penetrated, pierced, or entered; impossible to get into or through.
Both words are negatives. Impervious is formed from the negative prefix im- and the adjective pervious. Impenetrable combines the same prefix, im-, with the adjective penetrable, which in turn comes from the verb penetrate.
pervious: adjective. Allowing the passage of water, air, etc., through its substance; permeable. Freq. with to.
penetrate: transitive verb. To get into or through, gain entrance or access to, especially with force, effort, or difficulty; to pierce.
For example, using the words literally, one might say that cheesecloth is pervious to air and water, while a raincoat is impervious to water.
The words are used frequently in a figurative sense.
If something is impervious, things wash over it without entering. It remains sealed from outside influences. Something impenetrable is not only impervious, it resists efforts to pierce it, either literally, with a pointed object, or figuratively, with the mind.
Compare the uses of both words in the following quotations from the web:
Such a standard was originally developed to ensure that governments and other organizations could maintain electronic archives that would be relatively impervious to changes in technology.
Recruits become fanatics on the subject, impervious to argument, quick to cut themselves off from doubters.
After listening to the debate people made up their minds and were fairly impervious to new information.
Let your plans be dark and impenetrable as night, and when you move, fall like a thunderbolt. –Sun Tzu, The Art of War.
After 9,000 emendations to James Joyce’s notoriously impenetrable novel, a ‘smoother’ new edition is promised. –The Guardian
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