# What is the difference betwen [tag:predicate-logic] and [tag:quantifiers]?

Tag wiki for says:

Questions concerning predicate calculus, i.e. the logic of quantifiers

and for it says:

The quantifiers ∀ ("for all") and ∃ ("there exists") are what distinguishes predicate calculus from propositional logic.

These appear to be the same. I suggest that we alias one to the other.

• While in many way those two quantifiers are "what distinguishes" predicate from propositional logic (along with the rest of the term vs. predicate syntax), there are other quantifiers. Cf. provability logic for "bounded quantifiers", many other variants. – hardmath Feb 1 '15 at 19:15
• I think the problem is the wiki for (quantifiers), not the tag itself. – Git Gud Feb 1 '15 at 22:50

• I do not disagree with what you say regarding 'How to Prove It' not being mathematical logic, but it is, as you say, about logical reasoning. The 'logical reasoning' part is why I think it's not a stretch to say that the book is a logic book. Regarding the tag's wiki specifically, it starts with "Questions about logic and mathematical logic", and I would include HtPI questions in the 'logic' bit. If not, how would you tag a question like "What is the truth table of $P\lor Q$" asked in the context of HtPI instead of the context of propositional calculus in mathematical logic? – Git Gud Feb 1 '15 at 23:13
• We actually have a tag for that: (proof-strategy). If you would tag the question I made up above as (propositional-calculus) (there isn't a propositional logic tag), given that $\text{propositional calculus}\subseteq \text{logic}$, how would that be less severe than also tagging such a question with (logic)? What about the typical questions that ask to model english statements in predicate calculus? Those aren't mathematical logic per se, they are about modelling, but you need to tag them as (predicate-calculus) anyway. Do you think there's a need for a tag to encompass HtPI-like questions? – Git Gud Feb 1 '15 at 23:39