Why are there lowercase letters in TeX and LaTeX?

Question

Notice that the letters here are all uppercase. Is there any reason why we write TeX and LaTeX respectively? Is it for emphasis? Or does it just make it look similar to the staggered lettering of their logos?

Answer 1

From Donald Knuth's TeXbook, p. 1:

The correct way to refer to TeX in a computer file, or when using some other medium that doesn’t allow lowering of the ‘E’, is to type ‘TeX’.

The same is true for LaTeX and all others.

Answer 2

From the Wikipedia entry on the pronunciation and writing of "LaTeX":

The name is traditionally printed with the special typographical logo [...]. In media where the logo cannot be precisely reproduced in running text, the word is typically given the unique capitalization LaTeX.

The same goes for the word TeX.

Answer 3

There are a lot of reasons, but:

1. Firstly, I believe the most compelling reason is that the mixed-case forms are simply the most unlikely forms to be mispronounced or misconstrued. I believe this is why D.E.K. chose them.

   • If you write TEX, it’s likely to be confused with the name Tex and be pronounced “teks.” But if you write TeX, it’s clearly something of its own nature.
   • If you write LATEX, it’s likely to be confused with the word latex and be pronounced “lay-teks.” But if you write LaTeX, it's clearly something different — or at the very least it causes you to wonder upon first encounter.

2. Secondly, the lowercase e in TeX visually resembles the vertically-lowered uppercase E in the logo. So it’s a visual cue and reminder. And although the lowercase a in LaTeX doesn’t quite match the vertically-rasied smaller uppercase A in the logo, it does follow directly in the footsteps of TeX and extends that visual “language” of notation. XeTeX and XeLaTeX also follows in these footsteps.