McLachlan opens by declaring that current logic textbooks are in a 'chaotic state' and that his system, based on Berkeley's philosophy, will make the nature of mind 'as comprehensible to beginners as other branches of knowledge.' He warns that Berkeley's philosophy, though reputedly difficult, should be judged by its explanatory power rather than initial plausibility. The preface sets a confident, reformist tone, promising a method that can be adapted even to realistic thinking by treating Berkeleyan categories as intuitions.

The Berkeleyan Foundation

The treatise explicitly grounds itself in Berkeley's distinction between active spirits and passive ideas. McLachlan quotes Berkeley: 'Spirits are active, indivisible substances; Ideas [objects] are inert, fleeting, dependent things.' He modifies Berkeley's system, calling it 'Berkeleyism considerably modified,' and insists that a philosophy should be judged by its coherence and lucidity, not by surface paradox. The excerpts show him applying this framework to perception, arguing that what we call 'cubic space' is not real but a 'metaphor of perspective effacement.' He challenges realists to explain why we do not see cubic space in the sky or arrange stars by calculated distances, claiming the idealist answer presents no difficulty.

Perspection and the Illusion of Distance

In the section on perspection, McLachlan analyzes how we perceive distance. He argues that the sky is not spaced because the conditions for terrestrial space are absent. Using the moon and planets as examples, he notes that a slight parallax is observable with close instrumental attention, but the calculated distances are 'not conceivable as associative distance.' He concludes that heavenly bodies are 'extremely degraded, perspectively speaking,' and their noumena are in contact with our minds, though the contact is 'infinitely slight' compared to what it would be if we could travel to them. This argument draws on Berkeley's Theory of Vision and Dialogues, which McLachlan cites as the source of his main points.

Concretion and the Backs of Things

McLachlan introduces a category he calls 'concretion,' using a cricket-ball as an example. Turning the ball in the hand yields a series of discs, only one visible at a time; the whole object is an 'imaginary whole constructed in the intellect out of fragmentary experience.' He distinguishes concretion from inherence, association, and perspection. A striking claim follows: 'Things have no backs in the popular sense of the word.' When we turn a back to perceive it, it becomes a front. Everything is a 'flat upright surface,' and solidity can be imitated on a flat surface with nearly the same illusive completeness. He also discusses how two persons perceiving the 'same' object from opposite directions see numerically distinct objects, though they may be reduced to the same general idea.

Resistance and the Limits of Power

McLachlan defines resistance as 'a negative term signifying the limit of our power to alter primary experience.' Where our power ceases, resistance begins. He references Dr. Johnson's famous refutation of Berkeley—kicking a stone—and reinterprets it: the experiment merely showed that not all means are adequate to change all primary experience. Johnson's kick did not disprove idealism; it only demonstrated that his power was insufficient to alter the post. This reinterpretation is characteristic of McLachlan's method: he takes a common objection and turns it into support for his system. The excerpts suggest that the book consistently applies this strategy, using everyday examples to illustrate abstract principles.

The excerpts reveal a work that is both a philosophical treatise and a pedagogical manual. McLachlan aims to make logic accessible, yet his arguments are dense and demand careful reading. Readers should attend to his definitions of key terms like 'perspection' and 'concretion,' and note how he uses Berkeley's ideas to challenge common-sense realism. The book's structure—moving from metaphysical foundations to specific categories—rewards sequential reading, but the later sections on dialectic may be adaptable to other frameworks, as the preface suggests.