In lesson 5.3, we have “…sia una buona idea.” (I haven't gotten there yet, but it looks like “una buona idea” also appears in 6.3 and 19.1.
From the adjective lesson, however, I would've thought that this should be “una buon'idea”
Is it personal preference whether one uses the contraction or not? Is one more common than the other in written vs. spoken language, for example?
Thanks!