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Perceptions of the mind

                     impressions                                                                                       ideas                                                            

Arguments for the claim that all ideas are copies of impressions.

1. If some ideas are not copies of impressions, then we should be able to find an idea which we cannot trace to an impression.

2. But when we analyze our ideas, we always find that our ideas can be resolved into simple ideas, and all the simple ideas can be traced to an impression.

So, all ideas are copies of impressions.

1. If ideas are not copies of impressions, then a person lacking a sense organ, who would thereby lack the corresponding impression, should still be able to have the corresponding ideas.

2. But a person who lacks a sense organ is unable to have the corresponding ideas (e.g., a blind person has no ideas of color and a deaf person has no ideas of sound).

So, ideas are copies of impressions.

One contradictory phenomenon: the missing shade of blue

Section IV: Sceptical Doutbs concerning the Operations of the Understanding

Part I: "All the objects of human reason or enquiry may naturally be divided into two kinds, to wit, Relations of Ideas, and Matters of Fact."

p. 500 "All reasonings concerning matter of fact seem to be founded on the relation of Cause and Effect. By means of that relation alone we can go beyond the evidence of our memory and senses."

p. 503:  "These two propositions are far from being the same,  I have found that such an object has always been attended with such an effect, and I foresee that other objects which are in appearance similar will be attended with similar effects."

What reason do we have for inferring the second claim from the first claim? Because we think that the future will resemble the past. Are we justified in that claim? Hume says NO.

1. If inductive reasoning can be justified, then the claim that the future will resemble the past can be justified.

2. If the claim that the future will resemble the past can be justified, then it can be justified a priori or a posteriori.

3. The claim that the future will resemble the past cannot be justified a priori.

4. The claim that the future will resemble the past cannot be justified a posteriori.

So, the claim that the future will resemble the past cannot be justified.

So, inductive reasoning cannot be justified.

Defense for premise 3:

• 1. If a claim can be justified a priori, then the denial of the claim must entail a contradiction.

• 2. The denial of the claim that the future will resemble the past does not entail a contradiction.

• So, the claim that the future will resemble the past cannot be justified a priori.