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General Philosophy · Lecture 21 of 33 · 12:33

5.4 Scepticism, Externalism and the Ethics of Belief

Study guide

What this lecture covers

The lecture closes the unit on knowledge and scepticism by testing whether externalism about knowledge can survive sceptical pressure, and whether a clever linguistic move by Hilary Putnam can dissolve the brain-in-a-vat worry. It follows on from earlier lectures on the analysis of knowledge and externalist accounts of justification.

By the end, you should be able to explain why externalism does not fully defeat the sceptic, state Putnam's semantic argument against vat scepticism and its main weakness, and describe why Hume's appeal to the ethics of belief offers a more modest way of living with scepticism than trying to refute it outright.

Key ideas

Externalism about knowledge: knowing depends on reliable causal connections between the world and your faculties, not on being able to justify your beliefs from the inside; this lets dogs, cats and unreflective people count as knowers.
The God's-eye problem: even if externalism is true, you cannot know from your own internal perspective that your faculties are in fact working reliably, so sceptical doubt can still be raised about your own case.
Putnam's semantic argument: if you are a brain in a vat, the word 'hand' in your mouth would refer to hand-images, not real hands, so your statement 'there's a hand' would still come out true.
Objection to Putnam: the argument only works if your word 'hand' was learned while envatted; someone kidnapped and envatted after learning language from real hands would still mean 'real hand', so the sceptical worry returns.
Vertical vs horizontal scepticism: vertical scepticism questions the inference from perceptions to an external world; horizontal scepticism (the problem of induction) questions whether the future will resemble the past, and it survives even if you accept living in a vat or matrix.
The ethics of belief: rather than demanding certainty before believing anything, Hume's approach asks what we should believe given that suspending all belief is psychologically impossible.
Living with less than certainty: because animal nature makes us believe things without full internal justification, externalism fits naturally with accepting fallible standards instead of holding out for an unreachable ideal.

Before you watch

Be familiar with the analysis of knowledge and the externalism/internalism debate covered in earlier lectures in this course.
Know the basic brain-in-a-vat and matrix scenarios as standard sceptical thought experiments.
Recall Hume's treatment of induction, since the lecture contrasts it with vertical scepticism.

Check your understanding

Why does externalism about knowledge fail to fully silence the sceptic, even if it is true?
Explain Putnam's argument for why 'there's a hand' comes out true even for a brain in a vat, and state the strongest objection to it.
What is the difference between vertical and horizontal scepticism, and why does the lecture treat horizontal scepticism as potentially more worrying?
How does appealing to the ethics of belief change the terms of the debate with the sceptic?

Vocabulary

externalism (noun): The view that a belief can be justified by reliable facts outside the believer's own awareness.
Externalism lets a dog count as knowing without conscious reasoning.
reliable (causal connection) (adjective): Consistently producing an accurate connection between two things.
Externalism relies on a reliable causal connection to the world.
God's-eye view (phrase): A perfect, all-knowing perspective that a normal observer cannot actually have.
The God's-eye problem shows we can't confirm our own reliability from inside.
sceptical pressure (phrase): The force of doubt applied to a claim or theory to test whether it survives.
Externalism is tested against sceptical pressure.
semantic argument (noun): An argument based on the meaning of words or language.
Putnam's semantic argument focuses on what 'hand' would mean.
refer (to) (verb): To point to or stand for a specific thing.
The word hand would refer to hand-images in the vat scenario.
envatted (adjective): Placed inside a vat, as in the brain-in-a-vat thought experiment.
An envatted brain never had contact with real hands.
kidnap (verb): To capture and take someone away by force.
A person could be kidnapped and later envatted.
matrix (noun): A simulated reality generated by a machine, as in the philosophical scenario.
Living in a matrix is another version of vat scepticism.
ethics of belief (noun): The philosophical question of what we are entitled or obligated to believe, given our situation.
Hume's ethics of belief asks what we should believe without certainty.
suspend (belief) (verb): To hold off from forming a judgment or opinion.
It's psychologically impossible to suspend all belief.
fallible (adjective): Capable of being wrong or making mistakes.
We accept fallible standards instead of demanding certainty.
silence (the sceptic) (verb): To stop someone's doubts or objections from being raised further.
Externalism fails to fully silence the sceptic.
weakness (of an argument) (noun): A flaw that makes an argument less convincing.
The lecture identifies the main weakness of Putnam's argument.
worrying (adjective): Causing concern or unease.
Horizontal scepticism is treated as potentially more worrying.
terms of the debate (phrase): The framework or basic assumptions within which a discussion takes place.
The ethics of belief changes the terms of the debate.
close (a unit) (verb): To bring a section of study to an end.
The lecture closes the unit on knowledge and scepticism.
modest (way) (adjective): Not overly ambitious or extreme, reasonable in scope.
Hume's approach offers a more modest way of living with scepticism.
linguistic (move) (adjective): Relating to language and how words are used or defined.
Putnam makes a clever linguistic move against the sceptic.
unreflective (adjective): Acting without conscious self-examination or reasoning.
Externalism lets unreflective people count as knowers.

From the YouTube description

A series of lectures delivered by Peter Millican to first-year philosophy students at the University of Oxford. The lectures comprise the 8-week General Philosophy course and were delivered in late 2009.

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