Impressions and Ideas

"we may divide all the perceptions of the mind into two classes or species which are distinguished by their different degrees of force and vivacity. The less forcible and lively are commonly denominated thoughts or ideas. The other species want a name... Let us, therefore, use a little freedom and call them impressions" (p.)


Perceptions: Sense & Reflection

Simple Impressions of Sense (lively)


 Simple Ideas of Sense (faint copy)

(red, hot, solid, extension, etc.)


(1) Impressions of sense (red, hot, solid) ------------> Ideas of sense (red, hot, solid)

(2) Impressions of reflection (anger, sadness, hunger, abhorrence) --------> Ideas of reflection ((a) anger, sadness, hunger, abhorrence and (b) evil, virtue)



Simple Impressions of Reflection (lively)


Simple Ideas of Reflection (faint copy)

(i) anger, sadness, hunger, abhorrence, etc.

(ii) evil, virtue (from (i))



Simple Perceptions vs. Complex Perceptions


Complex Perceptions =

Combination of simple impressions (either kind) (lively)


Complex Idea (faint copies)



Ideas are associated in three ways:

(1) Resemblance

(2) Contiguity in time and space

(3) Cause and Effect


Hume's Fork

(1)  Relations of ideas (a priori)

(2) Matters of fact and real existence (a posteriori)


Two sources of justification for beliefs:


Reason: Deductive reasoning (a priori)

Senses: Observation (a posteriori)




Q. Do we have an idea of power or causation or necessary connection?


Idea of sense?


"When we look about us toward external objects, and consider the operation of causes, we are never able, in a single instance, to discover any power or necessary connection; any quality, which binds the effect to the cause, and renders the one an infallible consequence of the other. We only find, that the one does actually, in fact, follow the other. The impulse of one billiard ball is attended with motion in the second. This is the whole that appears to the outward senses." (p.)


Idea of reflection?


"[O]ur idea of power is not copied from any sentiment or consciousness of power within ourselves, when we give rise to animal motion, or apply our limbs, to their proper use and office. That their motion follows the command of the will is a matter of common experience, like other natural events: but the power or energy by which this is effected, like that in other natural events, is unknown and inconceivable." (p.)


No idea of sense or idea of reflection of power, or causation, or necessary connection.



(1)    "In all single instances of the operation of bodies or minds, there is nothing that produces any impression, nor consequently can suggest any idea of power or necessary connection." (p.)




(2) "[W]hen many uniform instances appear, and the same object is always followed by the same event; we then begin to entertain the notion of cause and connection... We then feel a new sentiment or impression, to wit, a customary connection in the thought of imagination between one object and its usual attendant" (p.)


(3)  "[T]his sentiment is the original of that idea which we seek for" (p.)


Cause = df. (1) object, followed by another, and where all objects similar to the first are followed by objects similar to the second

Cause = df. (2) if the first object had not been, the second never had existed

Cause = df. (3) an object followed by another, and whose appearance always conveys the thought to that other