Difference between two examples of there being food at the party is not clear

Question

This is stupid. The examples of the party are both the same. No action is being completed or not being completed. It is just a statement of existence that there "was" food at the party. So we need a better explanation for why in one case it would be "habia" and in one case it would be "hubo."

Answer

Hola Philip

I appreciate the difficulty to understand the difference between using the preterite and the imperfect tense. It is something that doesn't exist in English and for this reason, this is one topic that takes time to master; it takes a lot of practice.

These sentences are not stupid; these sentences reflect what natives say and this sort of action can be expressed both in the preterite and the imperfect, depending on what the speaker wants to emphasise. The difference is explained with quite a lot of detail after showing the first set of examples.

You can say "había mucha comida en la fiesta" if your intention is to "describe" something that was happening in the party or "hubo mucha comida en la fiesta" if your perception of having a lot of food in that party is different as in seeing this as something that had an end, so you consider that timeframe as something as completed. Here you see that time of having that party (and having lots of food) as something not connected to the present, something with an end.

The "había" option doesn´t take into account any time/completion; it is simply descriptive.

Saludos cordiales

Inma

Answer

Ha ha, I feel your pain! Maybe this would help:

Hubo would be used when discussing the party the next day.

Habia would be used when, say, you left the party early and 20 minutes later you are telling a friend about it. For you, the party is in the past, but in fact it is ongoing. Maybe your friend expressed interest in going so you provided the info on the food situation.

The example (further below) "It was foggy yesterday" is a bit less clear with respect to habia. Habia would be used, say, early in the morning when it had been foggy all the day before. There would be a slight tonal emphasis on "yesterday," as in, "When will this fog end!"

(If any of that is incorrect, please provide any corrections necessary)

I see I should have put this as a comment where the question was repeated below, I did not presume to post this as an "answer." (I've been wondering why questions are duplicated in grey, I guess that is the reason).

Answer

Hola William
Those different contexts are very valid as to justifying the use of one or the other. I would also say to have this in mind: when we use "había" it's as if we place ourselves in the past "while" that action was happening so you see it clearly in process in your mind; however when we use "hubo" we place ourselves in the past but at the very end of that action where we see it ending (not in process), it is as if we saw the result. 
Saludos a todos