On the Main Principles of the Fine Arts and Sciences is Moses Mendelssohn’s essay in philosophical aesthetics. It begins from the assumption that the human spirit has learned to imitate beauty—beauty as the ruling mistress of the sentiments—in works of art. Its central question is what the arts have in common, or, more fundamentally, what beauty is.
Mendelssohn considers and revises the imitation thesis associated with Batteux. To say that art imitates nature merely postpones the question; the question must be recast as asking what the beauties of nature and of art share. He rejects Hutcheson’s appeal to a special aesthetic sense as a deus ex machina that forecloses inquiry. The common feature, Mendelssohn argues, is sensuously perfect representation, a conception indebted to Baumgarten and Sulzer. “Sensuous” here does not mean merely that an object is perceived by the external senses. It means that an entire array of an object’s features is perceived all at once. Unlike the distinct intellectual representation of a triangle, in which parts and aspects are distinguished from one another, a sensuous representation is clear but indistinct: the object is grasped as a whole without its parts being analytically separated. Yet order and harmony can be perceived sensuously without being intellectually distinguished.
Beauty, or perfect sensuous representation, therefore concerns forms, orders, harmonies, and whatever can be represented to the senses as a perfection. This definition allows that the content represented may be ugly or repugnant, provided that the representation itself is sensuously perfect. Mendelssohn addresses the mixed sentiment that arises when the object represented is unpleasant: pain at the content can be outweighed by pleasure in the representation, in the mental activity it stimulates, and in the artistry displayed.
From this account Mendelssohn derives two necessary conditions for fine art and letters: faithfulness of representation, or imitation, and—more important—artistry, even genius, in the production of the work. He argues that individual beauties in nature are inferior to the beauties produced by the arts.
The essay also distinguishes the fine arts from the fine sciences according to the kind of signs they use. The fine arts—music, dance, painting, sculpture, architecture—work predominantly with natural signs. The fine sciences, or belles lettres—poetry and rhetoric—typically employ artificial signs. Mendelssohn treats this distinction as hardly absolute. The essay ends by considering ways in which the arts may borrow from one another, as in allegorical painting, or combine, as in opera.
Throughout, the essay is concerned with the principles that make beauty intelligible in both nature and art: the perfection of the object, the clarity and liveliness of sensible cognition, and the artistry that produces or represents that perfection. It is a concentrated philosophical essay rather than a full-length systematic treatise, and its argument turns on the idea that art does not merely copy particular natural things but imitates beauty by producing sensuously perfect representations.
It develops this definition by making beauty a predicate of representation rather than of the object taken in isolation. A thing is beautiful when its perfection is apprehended through a clear but indistinct sensible representation; the same object can be beautiful under one representation and not under another. This is why the essay can allow art to represent imperfect, fragmentary, or repulsive subjects without ceasing to be beautiful: the judgment falls on the completeness, unity, and liveliness with which the sensible manifold is presented, not on the moral or physical perfection of the subject matter. Aesthetic pleasure is accordingly not a blind sensation but the felt exercise of the mind in grasping order and harmony as a whole.
The essay uses this account to clarify artistic production. The artist does not copy a particular natural thing; the artist imitates beautiful nature by selecting, combining, and intensifying traits so that the resulting whole is more perfectly sensible than the scattered beauties of experience. Faithfulness and artistry are therefore not opposed: faithful representation requires truth to the object and to the medium, while artistry consists in making the representation vivid, coherent, and complete. Genius is not rulelessness; it is the power to produce such wholes, and the rules of art are derived from the effects of successful works rather than imposed beforehand.
The sign-theory has consequences for the fine sciences as well. Natural signs are closer to the senses and can produce immediacy; artificial signs depend on convention and therefore require greater care if they are to achieve the same liveliness. Yet the fine sciences are not inferior for that reason: poetry and rhetoric can compensate for the arbitrariness of words through the resources of language, and they can express thoughts and relations less tied to sensuous particulars. The distinction between fine arts and fine sciences is thus a distinction of means, not of dignity; both remain governed by the same principle of sensuous perfection.
The essay also treats the mixed sentiment as a test case rather than an exception. The displeasure belongs to the content represented; the pleasure belongs to the representation and to the mind’s activity in comparing, ordering, and recognizing perfection. The latter can prevail when the representation is sufficiently perfect and lively. Similarly, the combination and borrowing of arts are judged by whether the borrowed element is assimilated to the signs and capacities of the receiving art. The book’s significance lies in this tightly argued attempt to give a single principle for the arts and letters while preserving their differences: beauty is sensible perfection, aesthetic pleasure is the lively apprehension of that perfection, and the artist’s task is to produce representations whose unity, clarity, and expressive force make perfection sensible.
