So
- optional verbatim and prioritized terms (like Google once did it)
- optional logical operators (and, or)
- a separate input box for context (either, specific terms like "product", "shopping", "legal", or some assorted terms to indicate a field of meaning and/or associated concepts, time span, etc)
It's the latter, where the search engine may shine and users may evoke its sophisticated intelligence, but, please, don't reinterpret the principal search terms to concepts that maybe just related. I do understand that this may not be for everyone, nor may it be the sole interface, but there should be a niche for this.
Example, wanting to find something about the early press coverage of System/360:
- Search term: (IBM || "big blue") && System/360
- Context: news 1965,1966 computer