What does it mean that the top grid is a four-line essential element?

Four-line elements refer to the basic elements of China's ancient literary genre-poetry. In ancient poetry, each poem has four lines, each with five words. This is the so-called "four lines at the top". Elements refer to the basic elements of poetry, that is, the content that poetry creation must contain. Ancient scholars believed that a good poem must have the following four elements:

1. Theme: Poetry must have a clear theme or content, which can describe the natural landscape, express feelings, eulogize heroes, discuss society and so on.

2. Rhetoric: Poetry is a kind of language art, and the use of rhetorical devices can increase the expressive force of poetry, such as metaphor, exaggeration and antithesis.

3. Rhythm: Ancient poetry is characterized by flat and even rhymes, and the rhythm of poetry needs to conform to certain laws, which can increase the musical sense of poetry.

4. Emotion: Poetry is an artistic form of expressing emotions. The author should be able to express real feelings in his creation and make readers feel excited.

The above four elements constitute the basic framework of ancient poetry and are also the criteria for evaluating a poem. They are isomorphic, forming the aesthetic feeling and artistic characteristics of ancient poetry.