If the root word ends with 'ce' or 'ge', you must keep the 'e' and use the '-ible' suffix. For example, 'manage' becomes 'manageable'.
The '-ible' suffix is usually used if you can't hear the whole root word. For example, 'visible' has the suffix 'ible' as 'vis' isn't the whole root word.
The '-able' suffix is usually used if you can hear the whole root word. For example, 'adapt' becomes 'adaptable'.
Beta