Webster's: 1. a deductive scheme of a formal argument consisting of a major and a minor premise and a conclusion (as 'every virtue is laudable; kindness is a virtue; therefore, kindness is laudable') 2. a subtle, specious, or crafty argument 3. deductive reasoning

To use Syllogism, enter a syllogism, one line at a time, and then test conclusions or ask the program to draw a conclusion.

A syllogism as (mis)defined here is a (possibly empty) set of numbered premises. No term may occur more than twice. Exactly two terms must occur exactly once: these are the two 'end' terms, which will appear in the conclusion. Furthermore, each premise must have exactly one term in common with its successor, for some ordering of the premises.

Simple Example

10 Socrates is a Greek
20 all men are mortal
30 all Greeks are men
40 no gods are mortal

Syllogism will draw a conclusion from such a list, if possible, or test a conclusion of yours. Syllogism may make you feel computers are smarter.

Tricky Example

10 all mortals are fools
20 all Athenians are men
30 all philosophers are geniuses
40 all people with good taste are philosophers
50 Richter is a diamond broker
60 Richter is the most hedonistic person in Florida
70 all men are mortal
80 no genius is a fool
90 all diamond brokers are people with good taste
100 the most hedonistic person in Florida is a decision-theorist

Syllogism can find the one logical conclusion here. Can you?

Reference: H. Gensler, 'A Simplified Decision Procedure for Categorical Syllogisms,' Notre Dame J of Formal Logic 14 (1973) 457-466

Syllogism was written by Richard Sharvy in 1987 or so (he died in 1988). It was written in some kind of Microsoft BASIC for CP/M. A few years later I distributed a compiled, Microsoft QuickBasic version of that program for the Macintosh, called 'Syllogism?'. That program is unstable on MacOS 8.x and up. It wasn't a rock on earlier Mac systems either.

Syllogism 1.0 is closer to standard BASIC than its predecessor. It's tested stable under two free and publicly distributed implementations of BASIC. Making the source code compliant with two independently developed versions BASIC should yield a useful degree of portability.


Syllogism 1.0, as source code or compiled program, costs zero dollars. You may distribute it. You may distribute altered versions provided: 1) they work, 2) there is clear and prominent notification that you altered the program and how, 2) there is clear and prominent notification of the original authorship.

Crunchy Pickle Software ...Macintosh software that puts your tastebuds first.