Difference between します and されます

Question

I'm trying to figure out the exact difference in the usage of します and されます.

For example:

(something)画面が表示します。
(something screen) will display

画面が表示されます。
(the screen will be displayed)

Another example:

This will be deleted.

削除します。
削除されます。

When a person (noun) does something we use します。
されます generally means "it will be done".

But in a number of contexts I've seen this used interchangeably.

Can someone clarify? How are 画面が表示します and 画面が表示されます different?

Answer 1

The basic difference between します and されます is simple; します is active and されます is passive (and sometimes honorific).

• 紹介します。 I will introduce (someone to someone).
• 紹介されます。 I will be introduced (to someone).

However, since the subject of a Japanese sentence is often omitted, you may find cases where する and される appear to be interchangeable. For example 保存したファイル and 保存されたファイル are usually interchangeable ("saved file"). The former literally means "a file that someone saved", and the latter means "a file that was saved".

Likewise, 削除します and 削除されます can be used interchangeably in a file delete confirmation dialog:

削除します。よろしいですか?
[Your operation] will delete [the file]. Proceed?

削除されます。よろしいですか?
[The file] will be deleted. Proceed?

But note that these appear to be interchangeable because the subjects have been omitted. If there is an explicit subject, ^[?]ファイルが削除します only means something weird like "The file will delete something", whereas ファイルが削除されます means "The file will be deleted".

表示 is a transitive-only suru-verb, so 画面が表示します normally means "A display will show something (e.g., a button)". If you mean "A screen will show up", the normal way to say this is 画面が表示されます (literally "A screen will be shown").

Note: You may find many examples of intransitive 表示, such as メッセージが表示します, by googling, but I believe this is nonstandard. On BCCWJ, there are 729 instances of が表示されます and only 2 instances of が表示します. The 2 instances both look weird to me. Many examples of が表示します on the net should be machine-translated ones.

Answer 2

It seems your context is User interface (UI).

Microsoft's Japanese style guide (for UI Localization) offers the following advice:

In general, use active voice when the agent of action is person (user). Use passive voice when the action is automatically performed by computer from user‘s point of view.

Examples:

Open the file.

ファイルを開きます。

A dialog box is displayed.

ダイアログボックスが表示されます。

The program will restart the computer after the installation.

インストール後にコンピューターが再起動されます。

インストール後、プログラムによりコンピューターが再起動されます。