Make an assertion, support it with evidence, reasoning and an illustration if necessary, make a transition and move on to your next point. One must balance elaborating points with overloading the audience. Most textbooks go on at length here regarding spatial, versus logical, versus chronological patterns of organization. I generally just teach Plato's "clever butcher" analogy. Plato said that a clumsy butcher takes a chicken and hacks it all to pieces; makes a mess of the whole thing. A clever butcher, on the other hand, realizes that the chicken has natural divisions, called joints, and uses those to cleanly divide the chicken. So, when organizing a speech, I just tell my students to look for the natural divisions of the topic and organize it around those. If during practice the speech doesn't seem to flow properly, all they have to do is reorganize. I don't think it needs to be any more complicated than that.
One thing's for certain. When you're building a beautiful edifice, and you go to the emporium to buy materials, you don't just wheel your cart down the aisle and grab materials willy-nilly. You buy the tools and materials you need according to the blue print. Disposition is about establishing a blueprint which guides the making process.
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