Translation guide
Expressing that an action is done thoroughly, to the end, or without leaving anything undone.
The speaker wants to emphasize that an action is performed completely, without stopping partway, often with a sense of finality or exhaustion of the object.
Attach to the て-form of a verb. Indicates that the action is done completely, often with a nuance of regret or that something is finished (and cannot be undone). Very common in speech.
I did all my homework completely.
I've already read that book completely.
Attach to the ます-stem of a verb. Means to do something to the very end, exhaustively. Often used when the action has a clear endpoint or when resources are used up.
He ran the marathon completely (to the end).
I've completely spent all my money.
Adverb meaning 'completely', 'entirely'. Often used with verbs indicating change of state or completion. Implies that nothing of the previous state remains.
I had completely forgotten.
The town's appearance has completely changed.
Adverb meaning 'completely', 'perfectly'. Slightly more formal or emphatic than すっかり. Used when something is done without any flaw or remainder.
The problem has been completely resolved.
His explanation is completely wrong.
Attach to the ます-stem of a verb. Means to do something to exhaustion, use up, or do every possible instance of the action. Stronger than きる in terms of exhausting resources or possibilities.
He used up all his money completely.
I've done everything I can (completely exhausted all options).
The action is carried out so thoroughly that it results in a negative state, often destruction, exhaustion, or irreversible change.
Same pattern as above, but here the nuance of regret or negative outcome is stronger. Often used when something is broken, lost, or done unintentionally but completely.
I ate the whole cake (and now it's gone, maybe regretfully).
I completely threw away the important documents (by mistake).
When used with verbs like 疲れる (get tired) or 腐る (rot), it emphasizes complete exhaustion or total decay.
I'm completely exhausted and can't move.
〜てしまう focuses on the completion of an action, often with a nuance of regret or unintended result. 〜きる emphasizes doing something to the very end or exhausting something, without necessarily implying regret. 〜てしまう is more common in daily conversation.
食べてしまった (I ate it all up, maybe I shouldn't have) vs 食べきった (I ate every last bit, accomplished eating it all).
While 完全に means 'completely', it can sound stiff or overly formal in casual speech. In many everyday situations, すっかり or verb endings like 〜てしまう are more natural.
The fish has completely rotted.