part (mass noun) is close to "some", it means some but not all thing.
a part (countable) is a separate piece of something that you can combine with other pieces.
It has been always a problem for me to choose the right one.
For example:
I think there's always a part of you that doubts what you're doing.
But I can say "some part of you always doubts," so then it is not a separate thing and then why "a part" was used in the sentence?
The following are some of the common definitions for part
- a piece or portion of a whole
- an integral constituent of something ⇒ dancing is part of what we teach
- an amount less than the whole; bit ⇒ they only recovered part of the money
Both part and a part can be used to refer to a discrete countable thing
We teach several skills. Dancing is part of what we teach.
We teach several skills. Dancing is a part of what we teach.
Dancing is a discrete thing but can take either construction.
And both part and a part can be used to refer to a more general portion of a thing that is not countable
Part of the food [or money, or care] will be devoted to the poor.
A part of the food [or money, or care] will be devoted to the poor.
The portion to be devoted is not defined in these sentences as comprising a specific discrete section or item, but either construction is clear and appropriate. The addition of the article a may give a slight connotation that the portion may already be determined, but not necessarily.
The term parts, on the other hand, almost always refers to discrete items.
Speaker A: Parts of our efforts have been highly successful.
Speaker B: Which parts?
