It is most obvious, as the reader will gather from what has been advanced, that for guarding, to the greatest possible extent, against error in conclusions, it is necessary to take into consideration the character of the data from which we reason--and to do this, we must draw from the general sources of knowledge to which the Logic of the Schools refers us. If we happen not to possess an accurate acquaintance with these branches, we must draw upon the best notions we have of them, or apply such natural sagacity as we happen to possess. But whether the information we happen to possess be complete or partial, it is not well that we are left to apply it at random, without any definite mode of procedure; and if logic refuses to assist us, and gives only a vague reference elsewhere, we must endeavour to assist ourselves. The datum of all arguments is a proposition, an assertion, or denial; and to ascertain its truth (upon which the value of the whole reasoning depends) we have to do with the facts upon which it rests, and the terms in which it is expressed. For it may be here observed, that the truth or falsity of every proposition depends upon facts. To ascertain the general accuracy of facts, we have to appeal to received standards of certainty; and to fix the meaning of terms, we have recourse to a plain principle of definition. In the task of recognising truth, so necessary in examining the premises of an argument, one is wonderfully assisted by being familiarised with the sources of truth, and the mode of its discovery. In these operations the tutored and untutored may alike be assisted by simple general rules. If these rules prove not infallible in every case, they will prove successful in the majority of cases. Since general rules are the only, rules that the vast field of facts admits of, they are not to be rejected on light grounds. They enable us to set forth intelligibly the reasons of our own conviction, and to detect and expose the fundamental fallacies of apparent arguments. Since they direct us where the Logic of the Schools leaves us without a guide, their value is apparent. The logical management of the syllogism involves much abstruseness respecting 'genus' and 'species,' the 'quantity' and 'quality' of 'propositions', 'contraries,' 'sub-contraries,' 'contradictions,' and 'subalterns.' Stepping by 'illative conversion,' 'six rules to be observed with respect to categorical syllogism' next demand attention, followed hard by eleven moods which can be used in a legitimate syllogism, Viz.---- A, A, A, A, A, I, A., E, E, A, E, O, A, I, I, A, O, O, E, A, E, E, A, O, E, I, O, I, A, I, O, A, O.' In the middle of this abstract train march the 'undistributed middle' and the 'illicit process,' attended by four figures represented by the following mnemonic lines, which must be carefully committed to memory:'-- Fig. 1. bArbArA, cElArEnt, dArII, fErIOque prioris. Fig. 2. cEsArE, dAmEstrEs, fEstInO, bArOkO,* secundae.