Adjectives 3 - Order, Comparatives and superlatives

Order of adjectives

This is an area where there are some rules, but the rules are so difficult to apply that it is best for students to meet lots of different examples and try to develop a 'feel' for what sounds right.
Comparatives and superlatives
Some two-syllable adjectives worry students. They have learned the rule that with longer adjectives we use more or most ~ more difficult, most interesting. They then meet commoner and more common and they sometimes come across more or most used with monosyllabic adjectives where a native speaker is using them to give emphasis. For example:

Which is better - this example or that one?
> I'm not sure. This one is much more pure.

'purer' would also have been correct, but for some reason of emphasis the native
speaker chose more pure!