Reasoning on Natural Theology falls necessarily into two divisions. The _first_ is made up of arguments drawn from the world without us. The _second_, of arguments drawn from the world within[h]. Each path of reasoning is subject to a cross division. We may argue affirmatively to a definite conclusion. We may also argue negatively with the same end in view;--we may show how much more difficult and less tenable is the contradictory hypothesis. It would be an awkward and almost impracticable task to keep these kinds of reasoning far apart. The natural procedure of thought, is to combine, rather than to dissever, when we marshal facts for the purpose of a full and wide generalization. Yet it does seem practicable to mark every transition of thought distinctly; and, if clearly marked, the distinction may easily be kept in mind. With this precaution, it may appear allowable to treat Natural Theology in a more discursive manner than could otherwise be permitted. The object of so doing will be to divest discussion as much as possible of a dry, logical stiffness; and, by ranging round each topic[i] to look at it in various lights; a process which generally discovers both the weakness and the strength of reasoning. Any one who has read Plato will understand the advantage of Dialogue in this respect. A more familiar book, Coleridge's "Friend," is another apt illustration. Each of its series of essays takes a sweep of the kind; and each "landing-place" affords a rest to the reader, and a fresh beginning to the intellectual tour. Without venturing to copy the quaint invention of landing-places, the present writer intends making every Chapter the occasion of a fresh _start_. The separate trains of thought will thus proceed from distinct points, and travel by separate routes, so as to admit of full inspection in their progress. Each argument allowed by the reader to be valid, will finally link itself to its neighbours; and all thoughtful persons know how to estimate the strength of convergent conclusions. The writer trusts, also, that he may be allowed to escape the two alternatives,--either circumlocution, or the use of an objectionable pronoun _singular_, by employing the plural "_we_." This word may perhaps have a further good effect; it may remind both reader and writer that they are engaged as pilgrim-companions on a journey of joint exploration.