关于逻辑中‘+’‘=’‘>’等符号是否属于常量的技术问询

Hey there! Great question—this is such a common confusion when you start moving beyond basic intuitive logic into formal systems, so you’re definitely not alone in feeling weird about Tarski calling + a constant. Let’s break this down simply:

First, we need to expand what "constant" means in formal logic—it’s way broader than just "names for individual things" like 2. In logic, a constant is any symbol that refers to a fixed, unchanging entity—and those entities don’t have to be numbers or objects; they can be functions, relations, or other fixed "rules" too.

Let’s break down your examples:

• + is a function constant. In formal terms, a function is an entity that takes a certain number of individual inputs (here, two numbers) and maps them to exactly one output (their sum). Even though we think of it as an "operation" day-to-day, in logic, this operation itself is treated as a fixed, unchanging thing—just like the number 2 is always the number 2, addition is always the same mapping rule. It never changes depending on context, so it qualifies as a constant.
• = and > are relation constants. Relations are entities that connect multiple individuals (two, in these cases) in a fixed way. = always denotes the "equality" relation (two things being identical), and > always denotes the "greater than" relation between numbers. These relations don’t shift or vary, so they’re constants too.

Tarski’s point here is that in formal logic, we distinguish between symbols that can stand for different things (variables, like x or y that can be any number) and symbols that have a fixed, predefined meaning. 2, +, =, and > all fall into that fixed category—they never get reassigned to mean something else in the system, which is the core of what makes them constants.

Think of it like a toolbox: 2 is a specific nail (a fixed object), while + is a hammer (a fixed tool that performs a specific action). The hammer isn’t a "thing" in the same way the nail is, but it’s still a fixed, unchanging part of your toolkit—just like function and relation constants are fixed parts of the logical system.

So to wrap up: Yes, symbols like +, =, > are absolutely considered constants in formal logic. The "things" they denote just aren’t individual objects—they’re fixed functions or relations, which formal logic treats as legitimate, unchanging entities.

备注：内容来源于stack exchange，提问作者Harshit Rajput