Can You Trust Your Memory?

Do you remember where your beliefs come from? If not, you may have lost your knowledge.

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What beliefs do you have that you can’t remember where they come from?

Let me give you an example: I believe that it’s not healthy to eat right before sleeping (and I think I’ve had this belief roughly since high school). But why do I believe that? I couldn’t tell you. I must have read it at some point, or maybe my mother told me, or perhaps I heard it from some classmate.

Let’s assume that it’s true, that eating right before sleeping really is unhealthy. When I first came to believe this, I must have had proper justification, even if I don’t remember it now. So, since I believed something based on justification (and we are for now assuming that the belief is true), it would be accurate to say that, back then, I had knowledge. I knew that eating right before sleep is unhealthy.

But do I still know it, given that I forgot my justification?

Philosophers Fred Dretske and Palle Yourgrau (1983) wrote a very interesting paper where they asked just this question. They pointed out that we seem to assume that we can retain knowledge in the following way:

• At some time t1, you come to know some fact.