In writing, the English alphabet has two forms of letters: uppercase and lowercase. Here are the key differences between uppercase and lowercase letters:

• Uppercase letters: Also known as capital letters, they are larger than their lowercase counterparts and are used to start sentences and as the initial letter of a proper noun. They can also be used for abbreviations and to signal importance or significance. Examples of uppercase letters include A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, and Z.

• Lowercase letters: They are smaller than uppercase letters and are used for the majority of the actual text. They follow the first letter of a sentence or the first letter of a proper noun. Examples of lowercase letters include a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r, s, t, u, v, w, x, y, and z.

The terms "uppercase" and "lowercase" originated from the common layouts of the shallow drawers called type cases used to hold the movable type for letterpress printing. The glyphs of lowercase letters can resemble smaller forms of the uppercase glyphs restricted to the baseband or can look hardly related.

In summary, uppercase letters are used for the beginning of sentences, proper nouns, and abbreviations, while lowercase letters are used for the majority of the actual text.