Final answer:
Theodore Roosevelt developed his argument in his speech 'Citizenship in a Republic' by emphasizing the importance of active citizenship and inspiring individuals to engage in public affairs for the betterment of society.
Step-by-step explanation:
In his speech titled 'Citizenship in a Republic,' Theodore Roosevelt developed his argument by emphasizing the importance of active citizenship and the responsibilities that come with it. He highlighted the need for individuals to engage in public affairs and work towards the betterment of society. Roosevelt used powerful and persuasive language to convey his message, appealing to the listener's sense of duty and inspiring them to take action. By promoting the idea of citizenship as an active and engaged role, Roosevelt sought to encourage individuals to participate in the democratic process and contribute to the progress of the nation.