Responding to skeptics, Reid notes that our beliefs are formed by our very constitution (40-41). We cannot always give a justifying foundation for every belief (indeed, for most), yet only a fool would say we are irrational in holding beliefs a…z. In fact, to use modern parlance, our natural condition is a belief-creating mechanism (see his famous quote on p. 118); indeed, one created by God. Along the way Reid, to anticipate Nicholas Wolterstorff, gives a fascinating retelling of the history of modern philosophy (pp. 106ff, 244). He ends with a discussion on what counts as “First Principles.”
Thomas Reid was responding to the idealism of Locke, Berkeley, and Hume. In a nutshell, and woefully oversimplifying what they believed, they said that in every act of memory there are two objects, one mental object in my head and the external, mediate object in real life. One of the dangers of this thought is that the external object, when the process is pushed to the limit, is dropped, leaving only as real the internal objects.
Reid’s answer to skepticism came like a summer rain: God created my brain in such a way, assuming I don’t have a concussion or something, that he will not deceive me. If I can use the laws of logic and grammar to understand what the Skeptic says about something difficult then I can understand something simple as when the prophet Isaiah tells me that the Servant suffered for the sins of my people (to use an example from hermeneutics).
But someone can respond, “Well, how do you know your mental faculties are working accordingly?” There are several responses:
I can return the question, “They must be working well enough for me to understand your question.”
This was Reid’s answer: Forgo the question right away. Simply suppose he is merry. If you find out he is serious, then suppose him mad.
“Defines common sense as those principles which we use everyday but can’t give a reason for using, yet the not-using of them leads to absurdity. Thus, contrary to the Van Tillians who think Reid is an autonomous rationalist, common-sense is a mode of knowing, not a set of propositions leading to a foundation.”
“grounds our knowing in our own constitution. Contra Hume, we don’t need to give an explicit justification for knowing x; it’s in our very constitution (thus avoiding Hume’s idealism). Holds to first principles, but says we don’t need to account for them. They are part of our constitution and people who deny them use them to deny them.”
The book was actually…fun. Reid is among the foremost prose stylist of English philosophy (I suppose that isn’t a great feat). While this edition is abridged, it’s not really a problem as it is the referenced edition among current Warrant studies.