Simple past vs. Subjunctive of 'sollen' and 'wollen'?

Question

I'm having difficulties working out how you would identify the meaning of a sentence such as:

Manni sollte die Tasche nicht vergessen

Is that the indicative simple past for "Manni was not supposed to forget the bag" or the subjunctive for: "Manni should not forget the bag"? How would you tell the difference?

Likewise with

Ich wollte einen Hund bekommen

Is that "I wanted to get a dog" or "I would like a dog"?

Answer 1

Simple past and subjunctive of sollen and wollen have collapsed to one form. As a rule of thumb, sollte is more often subjunctive while wollte almost always simple past. So let's assume that there is no context:

Ich sollte gehen.

Technically, it can be both and you're unable to discern it for sure. Experience tells you: go for subjunctive.

Ich wollte gehen.

You cannot discern that either, but unless if you speak with someone from the beginning of the 19th century, this is simple past.

Most of the time, you'll have context:

Ich sollte schlafen, will aber noch eine Grammatikfrage beantworten (Subjunctive)
Ich sollte schlafen, wurde dann aber dennoch aufgehalten (Simple past)

Edit: Another point. Usually, it is not possible to use a subjunctive within a single main clause:

*Du nähmest das Buch.

Exceptions (for arbitrary verbs) are irreal whishes:

Wenn Du doch nur das Buch nähmest.

Most modal auxiliaries are exceptions, but they will shift in meaning:

Ich müsste gehen, wenn er käme. ("pure" subjunctive of "I have to go")
Er müsste bald kommen. (He's expected to come)

Sollen shifts into "should do it, good idea to do it":

Er soll gehen. (weak "he has to go")
Er sollte gehen. (it would be better for him to go)

I'll even go as far that "sollen" is like "möchte", which cannot be used as "pure" subjunctive anymore:

Ich sollte rechts fahren, wenn ich ein langsames Fahrzeug hätte.
Ich würde links fahren sollen, wenn ich ein langsames Fahrzeug hätte.

Those are different sentences, with the second one referring to the Rechtsfahrgebot (you ought to drive on the right lane when possible and if you would impede traffic on the left lane). It would be, however highly unusual to use würde+sollen.

Wollen, even though being a modal auxiliary, doesn't allow for that shift, so when it appears in a single main clause, it can only be interpreted as simple past.

Answer 2

In this particular case

sollte its a subjunctive for sollen.

"Manni should not forget the bag" you can dedicate it from the general meaning.

but you can use sollte in the "Perfekt" tense.

Example :

Ich sollte gestern zu hause bleiben

which means I had to stay yesterday at home or depending on context I should have stood yesterday at home

Answer 3

Manni sollte die Tasche nicht vergessen

This is the present subjunctive. 'Manni sollte' means 'Manni should have', and with the negation provided by 'nicht' the phrase would be 'Manni should not have forgotten the bag', indicating that the bag is already forgotten by Manni, though it should not have been.

One way to think of the indicative is that it has a more factual feel to it. 'Manni was not supposed to' implies that Manni broke an objective, external rule, whereas the subjunctive 'Manni should not have' implies a subjective scorning over what Manni did.

Ich wollte einen Hund bekommen

Ich wollte means 'I wanted to', so 'I wanted to get a dog' would be the best translation. If you wanted to say 'would like', you would use möchte.

You might like to use this page to understand the difference. Hope this helps!