Notes on Logic Notation on the Web
Peter Suber, Philosophy Department, Earlham College

This is a chart of the Adobe Symbol Font:

Logicians should be satisfied if the characters with a yellow background are supported in HTML. (Symbols with a white background have long been supported by HTML or are not whole "characters".)

This hope is now realized with HTML 4.0. See Alan Wood's excellent guide to the symbols available in HTML 4.0. So now energy must be shifted to Netscape and Microsoft. When will their browsers support this advance?

It's not enough that your personal browser support HTML 4.0. Your readers' browsers must do so as well. This day may be long in coming.

Until then, you can get all the symbols in yellow above if you specify the Symbol font in an HTML tag. For example, this code

p <font face="Symbol">&#201;</font> q
produces this output

p É q

Your reader must have the Symbol font installed, but this is assured for nearly all Windows users. The results are iffy for Mac and UNIX users. For a helpful table showing which codes produce which symbols, see Alan Wood's guide to the Symbol font.

Since most users can use one or both of the methods above, and get elegant, searchable text, it is no longer necessary to use GIFs or other image files for individual symbols. I plan to convert all my files from GIF symbols to Symbol font text symbols the next chance I get. (In the case of my logic course files, this means when I next teach the courses.)

What follows is the version of this page I had online before HTML 4.0 was announced. I no longer support or update it, but I retain it here for the minority of users for whom the methods above will not work.

So far HTML does not support most of the symbols that make up standard logic notation. I'd like to see this changed. While I don't detect much of a movement for this change, here are my notes in case others wish to help.

Relevant links

Logic symbols already supported by HTML

Apart from ordinary keyboard symbols sometimes used in logic, such as "~" for negation, "&" for conjunction, "v" for disjunction, "-->" for material implication, <--> for material equivalence, "|" for the Sheffer stroke, the following special characters are supported by HTML:

DescriptionSymbolHTML code
Alternate negation sign¬&#172
Raised conjunction dot·&#183
Null setØ&#216

Logic symbol GIFs

Ira Carmel and I collaborated to make the following logic symbol GIFs for use on the web. (Ira did the hard part.) Here they are, for the world to steal.

They were designed to fit nicely with a 12 point font. But remember that even if you elect to present your page with a 12 point font, your reader may override your choice with his or her browser settings. So if you use these GIFs in a text file, you might want to include a warning that they appear at their best with a 12 point font.

Material implication
Material equivalence
Negation of material equivalence
Negation of equality
Semantic consequence
Syntactic consequence
Existential quantifier
Universal quantifier
Set membership
Denial of set membership
Set intersection
Set union
Proper subset
One-to-one correspondence

Thank you, Ira!

For examples of files in which I use these GIFs, see nearly any of the electronic hand-outs for my courses on Symbolic Logic (elementary) or Logical Systems (advanced).

If you have any news or relevant links on this front, please let me know.

Ribbon] Peter Suber, Department of Philosophy, Earlham College, Richmond, Indiana, 47374, U.S.A. Copyright © 1998, Peter Suber.