If vs if then statements [duplicate]

This question already has an answer here:

• What is the difference between “if” statements with “then” at the end? 5 answers

What is the difference between an if and an if then statement? For example, what's the difference between:

if (condition)
   puts "Condition is true"
end

and:

if (condition) then
   puts "Condition is true"
end