In other words, though, being devoid of language, the child cannot frame a proposition expressive of belief; cannot say "sugar-plum was sweet;" yet the psychical operation of which that proposition is merely the verbal expression, is perfectly effected.

The experience of the co-existence of sweetness with sugar has produced a state of mind which bears the same relation to a verbal proposition, as the natural disposition to produce a given idea, assumed to exist by Descartes as an "innate idea" would bear to that idea put into words.
The fact that the beliefs of memory precede the use of language, and therefore are originally purely instinctive, and independent of any rational justification, should have been of great importance to Hume, from its bearing upon his theory of causation; and it is curious that he has not adverted to it, but always takes the trustworthiness of memories for granted.

It may be worth while briefly to make good the omission.
That I was in pain, yesterday, is as certain to me as any matter of fact can be; by no effort of the imagination is it possible for me really to entertain the contrary belief.

At the same time, I am bound to admit, that the whole foundation for my belief is the fact, that the idea of pain is indissolubly associated in my mind with the idea of that much past time.

Any one who will be at the trouble may provide himself with hundreds of examples to the same effect.
This and similar observations are important under another aspect.