The question of –able or –ible a few weeks ago got me thinking of other spelling conundrums. Is a course of action inadvisable or unadvisable?
Either, actually – but usage is changing and now seems to favour inadvisable.
Is there a rule for determining this? Sort of, but it’s not very helpful (like the one for –able versus –ible).
The general rule is where the word is fully English, go with un–. Example: unwholesome. Where the root is Latin (or more immediately so), the negated form generally takes in–, as in ineffable or inevitable.
This assumes some familiarity with word origins, however – and it may not always be easy to determine whether a word is more Latin than English. In those cases, you might go either way: it could be insanitary or unsanitary, for example.
The Latinity rule breaks down anyway. The root of both just and justice is Latin, but it’s fully acclimatised in English. This leaves us with unjust but injustice. Similarly, unable but inability. Maybe un– for shorter words and in– for longer ones? And yet, unexpressive but inexpressible.
Words ending in –ed and –ing tend to go with un—(undigested; unceasing, uncomprehending). Words ending in —ible usually take in—(inaccessible), but –able words don’t follow a regular pattern: inconceivable but unbelievable. For –ent, go with in—(infrequent).
The following could take un– or in– (for those marked with an *, the in– form is probably in the ascendant):
In the end, you just have to remember.
Next time: oh, with the verbing!