You might say you have a "bad memory" because you don't remember what cake you had at your last birthday party or the plot of a movie you watched last month. On the other hand, you might precisely recall the surface temperature of the sun any time when asked.

So, is your memory bad, or just fine? Memory is at the very heart of who we are, but it's surprisingly complex once we start looking at how it all fits together.

In fact, there's more than one type of memory, and this determines how we recall certain facts about the world and ourselves.

How do we classify memory?

Cognitive psychologists distinguish between declarative memory and non-declarative memory. Non-declarative memories are expressed without conscious recollection, such as skills and habits like typing on a keyboard or riding a bike.

But memories you're consciously aware of are declarative--you know your name, you know what year it is, and you know there is mustard in the fridge because you put it there.

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