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Better, worse, further, and less.
Why you specifically
The rule
English has a few comparative forms that do not add -er or use more. Good becomes better, bad becomes worse, far becomes further, and little becomes less. Use them in comparative sentences, usually with than.
The trap
This book is gooder than that one.
This book is better than that one.
Better is the comparative form of good. Use than after comparatives to show the second thing.
His pronunciation is badder than mine.
His pronunciation is worse than mine.
Worse is the comparative form of bad. Do not use badder in standard English.
We walked more far than we planned.
We walked further than we planned.
Further is a comparative meaning greater distance, and it is the standard form in this meaning.
I need fewer time to finish this task.
I need less time to finish this task.
Less is the comparative form used with uncountable nouns and amounts. Do not use fewer with time in this meaning.
Prove it
10 drills
You have not fought this one yet.
