Berkeley: The Argument for Idealism and the Argument Against Skepticism

Introduction and Context:  Locke and Primary and Secondary Properties
To really understand Berkeley's arguments, you have to understand what issues and positions he was responding to. Descartes left us with a problem:  Since we can never "get out of our own heads," how do we know that our ideas and perceptions of the external world of objects resemble what those external objects that cause our perceptions are actually like.   Locke calls our inability to directly perceive the external world the problem of the veil of perception (we only have direct access to our perceptions, not the external objects that cause those perceptions).  This general model of perception is called representationalism.

We're going to take a quick look at Locke because Berkeley is in large part responding to Locke's solution to this problem.  Locke's solution has both a metaphysical component (having to do with the nature of reality) and an epistemological component (how we can know about that reality). Beginning with the metaphysical, it goes something like this (condensed from 500 pages):

Locke's Metaphysical Argument First of all, our perceptions have to be of something. Something has to cause them.  The most likely candidate is "stuff out there" in the world (he calls it "substance"). Substances have properties like color, shape, taste, smell, spacio-temporal location, solidity, etc...  These properties can be divided into 2 categories:  primary and secondary. We can look at these two types properties as inherent and dependent properties (from the metaphysical point of view). I'll elaborate all little more after this example:

Consider the properites of color, extension, and shape to illustrate the difference.  Color is a secondary property (i.e., dependent) because it depends for its existence on the primary properties.  That is, you cannot have color just randomly floating around in the air.  If must exist in something extended and with shape (not to mention spacio-temporal location).  This is one argument for the dependence of color.

The other is that color is actually the result of the object's surface properties.  The object's surface itself doesn't have a color.  When light (full spectrum) hits an object's surface, the particular shape (at the atomic level) of the object's surface (i.e., extension) absorbs some light wavelengths and reflects others.  The wavelengths that are reflected are the ones that enter our retina and initiate a causal chain terminating with our perception of a color "in the theatre of our mind."  Recall, however, that the lightwave frequency that enters our retina isn't itself colored, it merely has a wavelength that activates certain receptors (e.g., ones that cause "yellow") rather than others (e.g., ones that cause "red").

So, lets quickly recap the metaphysical argument.
(P1)  Something outside of us must be causing our perceptions.
(P2)  It's most likely external objects which are made of or are substances (Locke isn't clear here).
(P3)  The qualities like extension, shape, quantity, etc...are necessary for the object to exist as a physical entity.  Lets call them primary qualities.
(P4)  The qualities like color, texture, taste, and sound depend for their existence on the primary qualities.  Lets call them secondary qualities.
(P5)  It's not possible for a secondary property to exist on its own, whereas primary properties can. These names are a good description of the qualities.
(C)   Substances have 2 classes of properties: Primary and Secondary.

The external objects that cause our perceptions have primary and secondary properties. Primary properties are objective and will be perceived regardless the nature of a perceiver's perceptual system or point of view because they inhere in the objects.

Now, lets put on our epistemologist hats.

How can we know about the external world based on our perceptions of it since all we have access to are the ideas inside our heads?  (I.e., how can we know that the properties that an external object have "match up" with the image we have of it projected in our heads)

Recall that the primary qualities include extension, solidity, motion, quantity, spacio-temporal location, and shape. All external objects, when they are perceived, must have these properties in order to be perceived.  For instance, could you perceive an object that isn't extended? (i.e., that doesn't occupy space?)  Could you perceive an object that has no shape?  Locke says "no," and this is evidence of the fact that primary qualities are necessarily in the objects we perceive rather than simply in our pointy little heads.  

We can therefore know that our perceptions of external objects and those external objects themselves "match up" in terms of primary qualities.  It follows that, we can know stuff about the primary qualities of objects in the world as well as about the relations between those primary qualities in objects.

Secondary qualities are subjective: that is, the way each individual perceives them is a product of how our particular perceptual system works.  It might very well be that my purple is your red and vice versa.  There is no way to ever know.  For this reason, our perceptions of secondary qualities don't give us any information about how the "real" world is outside of our perceptions.

Ok, I think that should be (more than) enough to get us started...

Berkeley's Idealism and Its Motivations
Key Idea:  "[. . .] the very existence of an unthinking being consists in being perceived."

We can summarize Berkeley's position like this:  The only thing we have direct access to with our minds is ideas (i.e., images, memories, perceptions).  This means that we can only know that 2 types of things are real and exist: ideas and the minds that perceive them.  Knowledge consists in the apprehension of the contents of our minds (ideas) and the regular relations between them.  Furthermore, the notion of "matter" or "material substance" is incoherent and therefore cannot exist.

Epistemological Motivation:
I'll get to it a bit later, but he further argues that we don't need to posit physical objects to explain how ideas get into our minds.  In fact, by not positing physical objects we completely avoid the epistemological problem of the veil of perception; i.e., trying to figure out if our perceptions of external objects match up with up with external objects themselves.  Also, we sidestep the veil of perception problem, we also avoid the problem of skepticism.

Metaphysical Motivation:
With idealism, we also avoid a metaphysical problem: supposing the there are only 2 types of things in the universe, matter and minds, how is it possible for these things to interact causally?  Consider the following:  matter has the properties of extension, shape, solidity, and most importantly a spacial location.   Minds on the other hand don't have any of these properties (extension, shape, solidity, nor do they exist in any spacial location), their only properties are ideas.  So how the crap can a physical object (i.e., matter) cause something to happen in a mind (which doesn't have any of the properties of matter)?  This problem is further exacerbated when we consider that matter can't have mental properties (ideas).

Destructive Arguments:  Why Positing Matter as the Cause of Ideas Is Incoherent
The first part of Berkeley's project is to show that the materialist conception of the world is incoherent.

Groundwork:  The Argument Against "Resemblance"
Before going directly after the materialist  conception  of the world (i.e., the position that there are physical substances), Berkeley lays down the groundwork with the following argument against the notion of resemblance between ideas and material objects:

Materialist say that our ideas of physical objects resemble the physical objects themselves.  For example, when I look at a cat, the idea (i.e., perception) which the actual cat causes me to have in my mind resembles the actual cat outside my mind.

Berkeley says this notion of resemblance is a mistake: the only thing that can resemble an idea is other idea.  Recall that ideas are something that minds have--physical objects can't have ideas.  That is, ideas have very different properties from physical things--ideas, unlike physical objects, don't have a spacial location, for example.  Because the properties possessed by physical things and the properties of ideas are so completely different, it is not possible for ideas to resemble physical things.

To repeat: the only thing that can resemble an idea is another idea.  From this it follows that extension can only resemble extension, solidity can only resemble solidity, color can only resemble color, and so on...  Ideas cannot resemble objects that have the properties of matter because ideas can only resemble ideas (and ideas don't have the properties of matter).

Collapse of Primary and Secondary Qualities Distinction
Recall that materialists (like Descartes and Locke) hold that not all properties have the same metaphysical and epistemological status.  Secondary properties only exist as a consequence of primary qualities.  Also secondary properties are a consequence of how our perceptual system works and are therefore subjective, while primary qualities are objective because we perceive shape, extension, quantity the same regardless of our perceptual system or point of view.

For example, you can't experience a circular object as triangular no matter how your perceptual system is configured because the circular shape inheres in the physical object whereas something like color isn't and is added by our minds.

Ok, so in this part of the argument (9-15 PHK) Berkeley wants to further show that the mere concept of a hierarchy of properties is incoherent:  All properties are metaphysically and epistemically equal.  And, contrary to the materialist hypothesis, all properties inhere in mind.

The argument goes something like this:  Try to imagine a physical object that possesses the "primary" properties of extension and motion.  Go ahead, do it.  Now, is it possible for you to do it without also imagining the object with some color, no matter how faint?  I don't know about you, but I can't do it.  Even if I just imagine the outline of a figure, that outline still has a color.

So, what does this mean?  What Berkeley does next is very clever.  He says, look youz guys (referring to materialists): You say that secondary properties only exist as ideas in the mind, but we have just shown that you cannot imagine a material object's primary qualities without its secondary properties (like color).  It follows that what you call primary (objective) properties require for their perception that there be secondary properties.  

The dependance relation between primary and secondary is mutual rather than only secondary depending on primary properties.  You cannot "abstract away" primary qualities from secondary qualities, both are required for perception of objects.  And since, as you say, "secondary" properties are mental, both primary and secondary properties must be mental because how could a physical property depend on for its existence a mental property?

Anti-Abstraction Argument
If that isn't clear, he gives another formulation of the argument which emphasizes the role of abstraction in Berkeley destruction of the primary/secondary distinction.   It goes like this:

The only way to conceive of the properties of pure extension or shape is to abstract them from a compound idea of an object (i.e. one with both primary and secondary qualities). Objects don't have "pure" extension or shape without color. We have to abstract those to properties out.  And when we engage in the act of abstraction, where do those "primary" qualities exist?  They exist only in the mind.  That is, since abstraction is a mental activity, pure extension and shape can exist only as ideas, and therefore those properties must be mental properties (i.e., ideas).

More Examples:
Quantity:  The materialists argue that quantity is an objective property of objects.  However, Berkeley argues it is clearly a subjective mental quality because something's quantity will depend on how we want to "chop it up."  For example, I might say my chair is 2ft high or 24" high or 60cm high.  The number I use to measure distance is totally subjective.

Likewise I might say there is one book, or 350 pages, or 345,660 words.  It's entirely up to me how I want to conceive an object of perception and what units I'd like to use to describe it.

The Master Argument for Idealism
In 22-23 (PHK), Berkeley gives what is called "the master argument" because he seems to think that even if you reject all the other arguments, this argument shows that the only place anything can exist is in the mind.  (And since anything that exists in the mind is an idea, the only things that exist are ideas and minds).  He begins: 

I am content to put the whole issue upon this issue; if you an but conceive it possible for one extended moveable substance, or in general, for any one idea or any thing like an idea, to exist otherwise than in a mind perceiving it, I shall readily give up the causes.

So what does all this mean?  Essentially, he is arguing that the only place anything can exist in is the mind as an idea. 

For example, can you imagine a color that is unperceived? Ah ha! No, you can't because in order to do so, you have to imagine it, and thereby perceive it in your mind.  Can you imagine an extended object that is unperceived?  Ah ha!  No you can't!  To do so requires that you imagine that object, thereby proving it exists in the mind, not "out there"!  It is impossible to think of a physical property or object that exists unperceived (outside the mind) because anytime you think do, ta da! you're perceiving it (as an idea).  

As Berkeley says, [you cannot conceive of anything existing outside the mind because doing so] only shows you have the power of imagining or forming ideas in your mind: to make out this, it is necessary that you conceive them existing unconceived or unthought of, which is a manifest repugnancy (i.e., absurdity).  

Implications of Idealism:  Minds and Ideas
If we agree with Berkeley's reasoning up to this point it seems we have to reject the notion of mind-independent objects.  What follows from this is that the only things that exist are minds (aka spirits, souls) and ideas (aka perceptions, conceptions, memories).  Minds are "active, indivisible substances" and ideas are "inert, fleeting, dependent beings."  Therefore, objects only exist as ideas in minds.  ([. . .] the very existence of an unthinking being consists in being perceived.) 

We know that we exist through internal reflection and introspection; we can know other minds exist through reason.  (This will present problems as we will see in the next post on Russell and the problem of solipsism.)

Possible Objection and Reply
One possible objection to the view revolves around how we explain where ideas of external objects come from.  If there are no external physical objects, what are causing my perceptions?  Berkeley replies that we can call the things which we perceive via our senses "external" in terms of their origin, but they needn't be composed of matter.  They exist and come from other minds.  In particular, from God's mind. So, if I close my eyes, the object I was looking at doesn't cease to exist, but continues to exist in God's mind.