I have happened upon this use of a in a video on english grammar. It is at around 7 minute and 35 second. Here it goes:
Fine wines, and a knowledge thereof, are luxury few can afford.
I am aware that when a mass nount used with an adjective then an article is needed, but there a mass noun is alone. Tell me please why the teacher decided to use a before the word. Does a mean a little there?
Consider the following sentence:
An understanding of internal combustion engines will help you in this job.
Why do we use the indefinite article an there?
Because no one person understands everything about this topic, which would warrant the use of the:
The understanding of internal combustion engines will help you in this job.
The implies there is only one "understanding" and it does not allow for partial understandings or multiple different understandings.
The king versus a king.
Instead of one perfect understanding there are multiple partial understandings of the topic which, although partial, still qualify as "understanding".
You can understand something without knowing everything there is to know about it.
Compare:
A cheerful disposition...
Not all cheerful dispositions are identical and monolithic:
The cheerful disposition.
Instead there are many different dispositions all of which could qualify as "cheerful" despite their differences:
A cheerful disposition.
A does not mean 'little'. We can use the indefinite article before otherwise non-count nouns when we are discussing a person's relationship to a particular topic or thing (e.g.) knowledge of/understanding of/acquaintance with/love of (etc). A dictionary entry that equally applies to the other nouns I mentioned: "Knowledge is sometimes used with a, but only in the pattern a knowledge of something (or a good/deep/thorough etc knowledge of something): Effective use of language necessitates a good knowledge of grammar." https://www.macmillandictionary.com/dictionary/british/knowledge
A knowledge of Japanese, an understanding of legal terms, a love of literature, an acquaintance with opera.
