判断 and 決断: assessing and deciding
Distinguish the basis for a judgment from the action decided on, and separate decisions from execution.
Assessing a situation
判断, read はんだん, means judging a situation or suitability based on information. 資料を見て判断しました。 means judging after examining the material.
今は判断できません。 says that a judgment cannot be made now. Do not expand this into a permanent inability.
Deciding on a course of action
決断, read けつだん, means making a decision about what to do. 留学することを決断しました。 means deciding to study abroad.
決断するまでに時間がかかりました。 says that reaching the decision took time. Read the eventual decision together with the deliberation beforehand.
Judgment and action as stages
必要だと判断して、購入を決断しました。 says that something was judged necessary and a decision to buy it followed. It links the judgment's content to the chosen action.
購入を決断しましたが、まだ注文していません。 says that the purchase was decided on, but no order has been placed yet. Decision and execution are separate stages.
Has ordering finished in 購入を決断しましたが、まだ注文していません?
Show the answer and why
No. The decision to buy has been made, but the order has not been placed.