Contemplating those sentiments of Humeís, it seems little and much has changed since he expressed them. In respect of comprehending how thought and thing are united, there has been no progress, unless the volume of material brought to bear on a problem counts as progress. It is as unclear now as then how thought actuates matter. With the rise of empiricism and the sciences, and the rationalisation of human activity (all scarcely visible when Humeís work was published), the influence of the habit of mind that uncovered the problem has waned as the scale of the mindís operations in the realms of gross matter has increased. The knowledge acquired since, of mind and the material world and of the determining relationships between them, has brought us no nearer understanding how they are attuned to each otherís difference. The question isnít pressing in the context of the kind of progress we seek; it isnít necessary to know how this or any relationship works for it to work. But not to know diminishes the humanist project, especially its pursuit of unity. And that is more or less how things stand.

From his reflections Hume returns to the practical question of how we learn one event will follow another, or an effect will follow a cause. Denying we ever find a connection between events that brings about this consequence, or can discover a power in things or causes that would account for it, he concludes we learn from experience. The constant conjunction of events accustoms us to expect instinctively one event will follow another. Thus in experiencing the efficacy of an act of volition we come to know of its influence on objects. We know of no link between mind and matter.

Though he appears at the head of this essay, Hume comes to the fore only occasionally. His ideas are not its subject. The theme of what follows is the indiscernibility of connections, and it has been redeemed from other contexts and pursued here because there is more to be said of it than its former situation allowed. Connections are sought now, not as a tangible presence that has so far eluded apprehension, but as a shift of aspect that cannot be apprehended by analytical methods. Consideration is given to how the indiscernibility of connections affects structures of relations and our understanding of them, especially the relationship between an observer and what is observed. The theme of indiscernibility eventually acquires a bearing on the issue of how the mind of an observer escapes from its conceptions or perceptions, via a link we canít apprehend, into a habitat apparently embodying them. The conclusion is that it escapes through an absolute shift (indiscernible to the observer) linking the aspects. Humeís thoughts on connections acquired a retrospective bearing on this way of seeing relationships. His use of the concept, present in the background, was eclipsed by the conviction that the shift linked things. Only late in the day did the thought occur that Humeís indiscernible link and the shift of aspect might be one and the same.

In the prose of the Enquiry, archaic resonances emerge within a recognisably modern pattern of expression, cogently argued and embodying rational goals. For Hume such transitions would have been natural. The conjunction of diverse strains is characteristic of the circumstances in which the shifts that form indiscernible links occur. The strain of resignation evident in the eighteenth century sensibility, even as it embarked on the great venture of rational enlightenment, registers a consciousness not simply of being at the point of departure from the past, but of still belonging to it. Hume's scepticism reflects an ambivalence. On the one hand a pessimistic acquiescence in the face of the inscrutability of reality, and on the other a resolve to employ scepticism to distinguish the vain from the useful inquiry and make progress in those areas in which it could be made. He and his peers form a link between a past vanquished by their legacy, and a future bequeathed to their heirs, one the price of the other. What has changed for us is the capacity of the language and sensibility to express a sense of the magnitude of what it does not and, in respect of those things undreamt of in its philosophy, cannot hope to understand. We no longer possess it, have become indifferent to what is beyond the reach of our understanding, and are incapable of seeing why we should regret the passing of a sense of humility in the presence of what diminishes humanity by its scale and incomprehensibility. The heirs of the enlightenment, having recast reality more or less in their own image, have little tendency to be in awe of it.

This essay doesnít attempt to give a scrupulously rational account of its subject. There were too many imponderables to justify that approach - and it was uncongenial to be bound so closely in these circumstances. But in spirit the enterprise was rational, to the extent it aimed to illuminate mystifying transformations and transitions currently accomplished without substantial means. If it achieves this, it should serve the cause of enlightenment.