Can we really rely on our senses?

The Scottish philosopher David Hume focused on this problem in his book An Enquiry into

Human Understanding, first published in 1748.

Hume was well known for his scepticism and his empiricism – the view that all knowledge

is derived from what we perceive via our five senses, rather than through reasoning and

theoretical speculation.

For Hume, our minds can only operate in four ways – compounding, transposing, augmenting

or diminishing materials received from the senses.

He believed that the only true statements we can make about reality are empirical – because

they are directly based on perceptions.

And he argued that we should be sceptical of general theories, since they are produced

by “customs of mind” – meaning habits of thoughts, rather than direct observations.

We have no guarantee, after all, that the world will continue to behave in the way it

has done in the past.

We can get a better grasp of Hume’s perspective on human understanding by looking at a child

playing with modelling clay.

Hume wrote that every thought we have consists of compounds of ideas – each directly derived

from sense perceptions.

It’s like a child sticking pieces of clay together – one is shaped like a piece of

cheese, two others like slices of bread. Together, they form something that our senses tell us

looks like a sandwich. Hume would add that any compound ideas we have about it – that’s

a big sandwich, that clay sandwich doesn’t look good to eat – are also derived from

sense perceptions.

The human mind, Hume believed, can transpose one complex idea onto another – generating

a new idea just as one piece of clay can be exchanged for another. For example, removing

a narwhal’s tusk and putting it onto a horse – making the idea of a unicorn.

According to Hume, the idea of God as a wise and powerful being is in fact nothing other

than the augmentation of certain qualities of our own minds, joined together into one

new idea.

Our minds, he thought, have nothing else from which to form an idea of God – just as our

child has nothing but clay to model with.

So although the human mind can mould all sorts of fantastical ideas, Hume states that, ultimately,

we are heavily restricted in what facts we can think – because these ideas must be

based on direct sense impressions.

Most importantly, though – Hume taught us that complex ideas should be viewed with scepticism

– because while we can explain their formation, we cannot prove their reality.

A more detailed examination of his ideas can be found in the MACAT analysis.