Difference between must_not and filter in elasticsearch

Question

Can someone explain to me what the difference between must_not and filter is in elasticsearch?

E.g. here (taken from elasticsearch definitive guide), why isn't must_not also used for the range?

{
    "bool": {
        "must":     { "match": { "title": "how to make millions" }},
        "must_not": { "match": { "tag":   "spam" }},
        "should": [
            { "match": { "tag": "starred" }}
        ],
        "filter": {
          "range": { "date": { "gte": "2014-01-01" }} 
        }
    }
}

Specifically looking at this documentation, it appears to me that they are exactly the same:

filter: The clause (query) must appear in matching documents. However unlike must the score of the query will be ignored. Filter clauses are executed in filter context, meaning that scoring is ignored and clauses are considered for caching.

must_not: The clause (query) must not appear in the matching documents. Clauses are executed in filter context meaning that scoring is ignored and clauses are considered for caching. Because scoring is ignored, a score of 0 for all documents is returned.

Answer 1

The filter is used when the matched documents need to be shown in the result, while must_not is used when the matched documents will not be shown in the results. For further analysis:

filter:

1. It is written in Filter context.
2. It does not affect the score of the result.
3. The matched query results will appear in the result.
4. Exact match based, not partial match.

must_not:

1. It is written again on the same filter context.
2. Which means it will not affect the score of the result.
3. The documents matched with this condition will NOT appear in the result.
4. Exact match based.

Answer 2

Basically, filter = must but without scoring.

must_not expresses a condition that MUST NOT be met, while filter (and must) express conditions that MUST be met in order for a document to be selected.