The central issue of question is the countable and uncountable usages of the words science and art.
Following are two common usages of science:
- (uncountable): All activity that we think of as scientific (that is, all research based on the scientific method).
- (countable): Any field of science (that is, any specific discipline of scientific research).
We might think about applying the same pattern as above to the word art.
Between usages of the two words, science and art, we find great similarity, but also a few differences.
Art is an activity, but it is one that produces objects.
Any of the following are common ways to refer to objects produced by artistic activity (such as drawings, paintings, or sculptures):
- Art (uncountable)
- Artwork (uncountable)
- Works of art (countable)
Not all kinds of artistic activity produce artwork.
- The visual arts are artistic activity that produces artwork, and include drawing, painting, and sculpting. (A visual art is any such field.)
- The visual arts are contrasted to the performing arts, which include music, dance, and theater. (A performing art is any such field.)
In some cases, we find that the word art confuses the activity with the objects.
As an example, the following two simple statements are not parallel:
- "I like science": From this statement, we understand that someone likes to study science.
- "I like art": From this statement, we think about admiring artwork, and lose the idea of studying. This loss gives us a reason to find a way to explain that someone likes to study art.
We need a way to refer to the activity of art, as distinct from artwork.
The arts are all activity that we think of as artistic.
As the arts is a countable usage, we also have the singular form. An art is any field within the arts, or sometimes, any field within only the visual arts.
Putting together the above, following are common usages of art:
- (uncountable): One or more objects of art, the same meaning as artwork.
- (uncountable): All activity within the visual arts (not including performing arts).
- (countable): Any field within the visual arts (not including performing arts).
- (uncountable): All activity within the arts (including performing arts).
- (countable): Any field within the arts (including performing arts).
Since science is all activity that we think of as scientific, we have no strong reason to use the term the sciences.
Yet, sometimes we want to emphasize the diversity and number of different fields, or to create a feeling that is general but also grand.
The sciences has the same meaning as science, but has a specific feeling that makes it uncommon except in certain literary contexts.
We can conclude with the following:
- Science is the common way to express all activity that we think of as scientific.
- The arts is the common way to express all activity that we think of as artistic.
For degrees, like a Bachelor's degree, we emphasize the activities, science and the arts. We call the degrees Bachelor of Science and Bachelor of Arts. In titles, we often omit articles, otherwise we would use Master of the Arts. Master of Sciences would feel too general, as though someone had studied every field of science for a long time.
This patterns appears elsewhere.
Following are two examples, both related to the US government:
The National Science Foundation and the National Endowment for the Arts are both agencies of the government. (The NSF might have been called the National Foundation for the Sciences, but this name may seem to emphasize the fields and their differences, rather than all of science together as a valuable pursuit.)
The Constitution lists the powers of Congress.
It describes one of the powers in the following text
(Article I, Section 8, Clause 8):
To promote the Progress of Science and useful Arts, by securing for limited Times to Authors and Inventors the exclusive Right to their respective Writings and Discoveries;
(Note that capitalization rules are different today than during the earlier period, which treated important common nouns the same as names and other proper nouns.)
The text means that Congress has the power to pass laws related to intellectual property ("securing", "exclusive right"), specifically for copyright ("the arts", "authors", "writings") and for patents ("science", "inventors", "discoveries").