応用 and 実用: Applying a method and suitability for use
Compare applying a learned method to another problem with a prototype’s practical suitability and a bag chosen for practicality.
Applying a method to a different problem
応用 means application. 「授業で習った方法を別の問題に応用した。」 states that a method learned in class was applied to another problem. Read the relationship between that method and its new target.
「基礎を理解してから応用問題に進みます。」 places understanding the basics before moving to applied problems. It does not say every problem has already been answered or the learning is finished.
Suitability for actual use
実用 concerns practical use or practicality. 「試作品がようやく実用に耐える段階になった。」 says the prototype has finally reached a stage suitable for actual use.
「見た目より実用を重視してかばんを選んだ。」 states that a bag was selected with practicality valued over appearance. It gives a selection criterion, not a price or quality score.
Application and practical suitability
The 応用 examples concern where a method is applied. The 実用 examples concern suitability for use or the criterion for selecting an object. Their glosses may overlap, but the focus in each sentence still matters.
A prototype being suitable for practical use does not establish completed mass production or sales. Applying a method to a different problem also does not guarantee that every application works well.
What do applying a method with 応用 and a prototype reaching 実用に耐える段階 each describe?
Show the answer and why
応用 describes applying a learned method to a new problem. 実用に耐える段階 describes the prototype’s suitability for actual use. Distinguish the application activity from the level of practical suitability.