text: Formal logic is interested in deductively valid arguments, for which the truth of their premises ensures 
  the truth of their conclusion. This means that it is impossible for the premises to be true and the 
  conclusion to be false.[11] For valid arguments, the logical structure of the premises and the conclusion 
  follows a pattern called a rule of inference.[12] For example, modus ponens is a rule of inference 
  according to which all arguments of the form "(1)*p*, (2) if*p*then*q*, (3) therefore*q*" are valid, independent 
  of what the terms*p*and*q*stand for.[13] In this sense, formal logic can be defined as the science of valid 
  inferences. An alternative definition sees logic as the study of logical truths.[14] A proposition is logically 
  true if its truth depends only on the logical vocabulary used in it. This means that it is true in all possible 
  worlds and under all interpretations of its non-logical terms, like the claim "either it is raining, or it is 
  not".[15] These two definitions of formal logic are not identical, but they are closely related. For example, 
  if the inference from*p*to*q*is deductively valid then the claim "if*p*then*q*" is a logical truth.[16] 