Some officers of the court are not persons who respect the law. A valid argument must have a true conclusion. If the premises in a valid argument are true, then it is possible for the conclusion to be false. If you know the extension of a term, you can always determine the intension of the term. Two co-referential terms can be substituted salva veritatae in all contexts.
All inductive arguments are invalid.
Sentences are the primary bearers of truth. In order for a set of statements to qualify as an argument, most of the statements in the set must be declarative statements. The relation of logical consequence obtains between the premise set and the conclusion in a valid argument. Any time that you cannot determine the extension of a term, that term has empty or null extension. A bi-conditional is equivalent to the conjunction of two conditionals.