modal verbs - Can vs. Could in the reply "It can/could be in the car"

I’ve made another mistake in a modals test, in the can/could segment. The following exchange was presented:

Where’s my bag? Have you seen it? – No, but it _ be in the car.

I decided that both ‘can’ and ‘could’ are appropriate in the underscored position. The key contained only ‘could’. I’m curious why ‘can’ here is wrong:

Where’s my bag? Have you seen it? – No, but it *can be in the car.

In the Russian language, we use only the present-tense form of ‘can’ in such hypothetical answers: the past of 'can' would sound literal and ridiculous; so one may tend to carbon-copy the 'can' construction into English, failing to notice the difference in sense.

I’ve consulted a textbook and it says that ‘can’ tends to be used to convey a more general meaning. An example is given:

The weather can change very quickly in the mountains. (in general)

The weather is nice now, but it could change. (the weather now, not in general).

Is it in the same vein with the car in the example? Does “It can be in the car” sound too general while “It could be in the car” zeroes in on the immediate situation?

Would the sentence with ‘can’ come out too haughty in the context, that is, a person turns for advice concerning situation at hand, and gets a generic sentence, almost telling him “well, your bag, speaking generally, can fit in the car, go guess the rest of it”?

Answer

Modal verbs can be a little tricky. When you suggest a possibility for a specific situation at hand, such as "Where is my bag (right now)?" you are hinting at where you think it "might" be. Since you are only talking about the bag in this specific instance you should use "could" or "might" to indicate you are responding to this situation. As you also correctly discovered, "can" is reserved for "general truths" (a kind of zero conditional: "If you smoke too much it can kill you").

The examples your textbook gave you are good. Try to contrast "right now/this specific situation" = "could" vs. "in general" = "can", as a rule of thumb.

To answer the last part of your question, "can" just doesn't really fit in this situation. Since you were asked about a specific situation "Where's my bag?" you really can't use "can". You can be plenty haughty by choosing your phrasing rather than your modal:

No, but it could be in the car along with your head that you clearly left there!

Lastly, and just a piece of advice, from the way I view "can" and "could" as possibility modals: Don't think of them as present and past (like when they describe ability/permission), but rather: general = can, specific = could.