# What is the difference between relational logic and predicate logic?

I am studying the Introduction to Logic course from Stanford University and I began learning about relational logic. However when I searched on google for the terms there I end up often with results from websites that teach predicate logic.

Is there a difference between the two types of logic?

• If these lecture notes from Stanford are about what you call "relational logic" then it is just another name for predicate calculus. There used to be something else called relational logic (or logic of relatives) developed by De Morgan and Peirce in 19th century (logic of intensional predicates in modern terms) but it is a rather niche subject today. Commented Jan 24, 2017 at 18:54
• @Conifold Indeed THAT is the course I am learning now. So I can consider that I am learning predicate logic right ? Commented Jan 24, 2017 at 19:00
• No difference; see page 1. Commented Jan 24, 2017 at 19:54
• @MauroALLEGRANZA Thanks for pointing out. Commented Jan 24, 2017 at 21:06
• @Conifold That should really be an answer (the potential ambiguity is worth having in an answer to the question, since it's not in the existing answer). Commented May 29, 2020 at 21:11

Relational logic is, in all likelihood, a subset of predicate logic and has to do with, as the name implies, relations.

Examples:

1. Jones (j) is Smith's (s) brother. Bxy = x is brother to y. So Bjs. This relation is symmetric i.e. Bjs implies and is implied by Bsj

2. Brown (b) is as fat as Smith. Fxy = x is as fat as y. So Fbs and also Fbb (the relation is reflexive)

3. Smith is taller than Jones. Txy = x is taller than y. So Tsj. Now for some relational logic: (Tsj & Tjb) implies Tsb (the relation is transitive).