This week we answer skeptics like Descartes with empiricism. Hank explains John Locke’s primary and secondary qualities and why George Berkeley doesn’t think that distinction works — leaving us with literally nothing but our minds, ideas, and perceptions.

PBS Digital Studios wants to get to know you better! If you have 10 minutes, we’d really appreciate it AND you’ll be entered for a chance to win a t-shirt!

Images and video via VideoBlocks or Wikimedia Commons, licensed under Creative Commons by 4.0:

Produced in collaboration with PBS Digital Studios:

Crash Course Philosophy is sponsored by Squarespace.

Want to find Crash Course elsewhere on the internet?
Facebook –
Twitter –
Tumblr –
Support CrashCourse on Patreon:

CC Kids:


  1. everyone's perception of the world is linked to one another, therefore, the world still exists. It's like 'perception' is being handed from a generation to a generation and from one person to the other ?

  2. If you are interested in logic and the depth of this (if you are free) check out Athenes logic debates and you will learn ALOT and be detached to things like bad habit without feeling bad instead happy

  3. I'd also like to point out that Berkeley attacks the distinction between primary and secondary qualities within his dialogue between Hylas (Objection to Berkely) and Philonous (Berkeley) with these points :

    1. What looks small to me may look huge to a small animal (So size is in fact subjective)
    2. What looks small from a distance looks large when viewed up close (Again comments on the mutable nature of the 'primary quality' size)
    3. What look smooth to the naked eye appears craggy and uneven under a microscope (Indicating that texture is not innate in the object)
    4. If you look at a circle straight on, it indeed looks circular. But if we look at it from an angle, the circle may appear t be oval. We see it differently, but it doesn't change.
    5. Motion arguably isn't constant. We measure the speed of motion by how quickly our minds work – to a creature that thinks much faster than us, e.g a fly which sees our movements In slow motion.

    I hope this was helpful! These videos are great, but if anyone was looking for further information about how Berkely denies the disparity between primary and secondary qualities, claiming that acctualy both primary and secondary qualities are subjective and surseptible to change through varying perceivers- than I'm sure this will help explain it better!!

  4. Taste texture color etc are all primary qualities, though, the symbol for representing them could be debated. Well, some people are color blind, and color blindness could be minimal or serious, but you can take a photograph or sample of the apples juice and measure these things.

  5. Hank, you're mispronouncing 'Berkeley'. It's actually pronounced 'Bar-clee', like the Basketball player Charles Barkley.

  6. "To be is to be perceived" is acutally in consense with quantum physics, and the denial of matter also kind of fits in this scheme. I really like this concept of God as the ultimate perceiver, thanks for this information!

  7. I feel Berkley's conclusions can also allow for athiesim, if our secondary qualities exist when perceived, essentially, we still exist, but we have no determined qualities, unless percieved, in a state not unlike how quantum particles operate. An electron, or other quantum particle exists as a cloud of probability, of possible locations, and it could be argued that it exists all throughout the cloud, and has only a couple properties, until it is percieved by a detector, then all of its other qualities must then collapse to the most likely state when it is observed. I think Berkley's logic allows for this, and in fact is slightly flawed, as I feel it would make more sense for it to be analogus to quantum mechanics, as it is a phenomenon we have observed happening, albeit indirectly, as by its very nature it is impossible to observe the probability wave without it collapsing into a particle

  8. Surely instead of primary qualities not existing it just means that secondary qualities are fixed and not based off perception. An apple will always have the same or similiar texture etc.

  9. is it just me or does this remind you guys a bit of the uncertainty of Quantum physics which occur when you observe or don't observe an object

  10. Does anyone have any link to any websites where I could learn all of this stuff deeper? Where I could get more info?

  11. I think what Berkely is referring to when he talks about primary qualities is objective measurements which yield the same result every time you perform them, where secondary qualities are more like subjective opiniony stuff that we don't really have a clearly defined scale for. An apple's redness can actually be measured in colour codes which under the same light conditions will yield the same number, but if we go into the wishy washy territory of "sort of redish-purple I think?", chances are that people will give different answers each time because there is no objective scale for them to test the redness to. That would be the same if we didn't have a scale for size. How big is the apple? Eh, pretty big I think, compared to the last apple I ate. That's also going to yield different results each time you ask someone because there's no way for them to objectively determine the size.

    If you don't have an objective scale to measure something with, it's really difficult to explain what it's like to someone else because you have to rely on your own experiences of the object, and that's where it becomes weird. How something feels is not measurable yet, so there is no scale, no interpersonally defined language we can use to describe the thing we're thinking of. We don't yet understand how sensory imput translates to experiences into conciousness so we can't figure out how something feels except for ourselves, and that's why we can't explain it. Try to explain the colour red to a blind person for example, it can't be done. That's the same for any experience that we don't have a pre-arranged scale for that the other human you're talking to can understand too.

    Conciousness is an absolutely weird thing and every time I try to figure out how it works I just get a headache.
    Speaking of which, auch… XD