The suffixes '-ably' and '-ibly' are used to make verbs into adverbs.
The '-ibly' suffix is usually used if you can't hear the whole root word. For example, 'possibly' has the '-ibly' suffix as 'poss' isn't the whole root word.
The '-ably' suffix is usually used if you can hear the whole root word. For example, with 'reliably' you can hear the whole root word 'rely'.
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