What exactly is the difference between the is_callable and function_exists in PHP?

Question

I am working on a project, in which I am using a deprecated function from the older version. But don\'t want my script to stop if used in the older version.

So I am check

Answer 1

If a function Plop exists then function_exists("Plop") will return true.

See function_exists

If a variable is callable then is_callable($var) will return true.
Now this could mean that $var is a function name.
But i could also be an object and method name combo.

See is_callable