Rhetoric distinguishes a listener who is simply uninformed from one who is uncertain or openly resistant. Ordinary information may need a plain assertion; doubt may call for clarification or emphasis; persistent denial may call for stronger expression.
Plain assertion: «زَيْدٌ قَائِمٌ» means that Zayd is standing, without an added particle of confirmation.
Emphasized assertion: «إِنَّ زَيْدًا قَائِمٌ» adds the particle inna to reinforce the statement.
No fixed number of emphatic devices suits every instance. The general lesson is that the form of the assertion can respond to the hearer's state.