able or ible?

A spelling activity with an older learner, sparked a little research in our lesson this week. We were looking at the root word 'struct' - from the Latin to build, fit together or an adjustment. We started thinking about prefixes or suffixes (to put at the start or at the end of the root word) and came up with con-struct (to build), de-struct-ion and even in-struct; a less obvious one but you can instruct someone to build something. In a Lego con-struct-ion kit, there are in-struct-ions on how to build the model!

Con-struct-ive criticism should build your confidence up, rather than de-struct-ive criticism which could tear you down. A struct-ure is a building, a noun, a thing.

Then my student wrote 'able' as in in-de-struct-able. But was this correct? Some words are spelt with the -able suffix and some are spelt with the -ible suffix. Which should we use?

It is all to do with whether the root exists on its own in our language. 'Teach, reach and measure' all do, so we can use 'able' as a suffix.

However, 'struct' and 'aud' do not. Something can be 'audible' and something can be 'constructible' but we don't use 'struct' and 'aud' on their own.

This technique of word inquiry, eytmology (where words come from) and morphology (how words contain units of meaning) can be a game-changer for learners and encourages independent research!