- Introduction
- Metaphysics vs. Physics
- Objectives of the Theory
- Distinction Underlying the Theory
- Presentation of the Theory
- Streaming Video Presentation of the Theory
*Principia Metaphysica*- Tutorial on
*Principia Metaphysica*

The equations at the top of this page are the two most important principles of the theory of abstract objects. The first principle expresses the existence conditions for abstract objects; the second expresses their identity conditions. In this document, we try to give you some idea of what these principles say.

The theory of abstract objects is a metaphysical theory. Whereas
physics attempts a systematic description of fundamental and complex
concrete objects, metaphysics attempts a systematic description of
fundamental and complex abstract objects. Abstract objects are the
objects that are presupposed by our scientific conceptual framework.
For example, when doing natural science, we presuppose that we can use
the *natural numbers* to count concrete objects, and that we
can use the *real numbers* to measure them in various ways. It
is part of our understanding of science that *natural laws*
exist (even if no one were around to discover them) and that the
*states of affairs* that obtain in the natural world are
governed by such laws. As part of our scientific investigations, we
presuppose that objects behave in certain ways because they have
certain *properties*, and that natural laws govern not just
actual objects that have certain properties, but any physically
*possible* object having those properties. So metaphysics
investigates numbers, laws, properties, possibilities, etc., as
entities in their own right, since they seem to be presupposed by our
very understanding of the scientific enterprise. The theory of
abstract objects attempts to organize these objects within a
systematic and axiomatic framework.

It would be a mistake to think that a theory postulating abstract objects is incompatible with our theories of natural science, which seem to presuppose that the only things that exist are the things governed by our true scientific theories. To see that the theory of abstract objects is compatible with natural scientific theories, we only have to think of abstract objects as possible and actual property-patterns. These patterns of properties objectify a group of properties that satisfy a certain pattern. For example, it will turn out that the real number π can be thought of as the pattern of properties satisfying the open sentence "According to the axioms of real number theory, π has the property F" (where "F" is a variable ranging over properties). There are an infinite number of properties satisfying this pattern (and an infinite number that don't). Our theory of abstract objects will "objectify" or "reify" the group of properties satisfying this pattern. So, on this view of what abstract objects are, we need not think of them as some ghostly, imperceptible kind of nonspatiotemporal substances. Instead, they are possible and actual patterns that are grounded in the arrangement of particles in the natural world and in the systematic behavior and linguistic usage of mathematicians and scientists as they discover, state, and apply theories of the natural world.

We can summarize the principal objectives of the theory of abstract objects as follows:

- To describe the logic underlying (scientific) thought and reasoning by extending classical propositional, predicate, and modal logic.
- To describe the laws governing universal entities such as properties, relations, and propositions (i.e., states of affairs).
- To identify
*theoretical*mathematical objects and relations as well as the*natural*mathematical objects such as natural numbers and natural sets. - To analyze the distinction between fact and fiction and systematize the various relationships between stories, characters, and other fictional objects.
- To systematize our modal thoughts about possible (actual, necessary) objects, states of affairs, situations and worlds.
- To account for the deviant logic of propositional attitude reports, explain the informativeness of identity statements, and give a general account of the objective and cognitive content of natural language.
- To axiomatize philosophical objects postulated by other philosophers, such as Forms (Plato), concepts (Leibniz), monads (Leibniz), possible worlds (Leibniz), nonexistent objects (Meinong), senses (Frege), extensions of concepts (Frege), noematic senses (Husserl), the world as a state of affairs (early Wittgenstein), moments of time, etc.

Further Explanation of the Objectives of the Theory

**The Distinction Underlying the Theory**

The theory is based on Ernst Mally's distinction between exemplifying
and encoding a property. This is a distinction between two
fundamental kinds of predication, and it is formally represented in
the theory as the distinction between the atomic formulas
‘*Fx*’ (‘*x* exemplifies
*F*’) and ‘*xF* ’ (‘*x*
encodes *F*’). The formula ‘*Fx*’
represents the classical kind of predication; it is used to logically
analyze such simple sentences as ‘John is happy’,
‘Clinton is president’, and ‘Socks is a cat’.
Mally's idea, in essence, was that we should *not* represent
sentences about fictional objects, such as ‘Sherlock Holmes is a
detective’, ‘Pegasus has wings’, ‘King Lear
had 3 daughters’, and ‘Zeus lived on Mt. Olympus’,
in terms of the notation ‘*Fx*’ (only real,
concrete objects can exemplify the properties of being a detective,
having wings, having daughters, or living on
Mt. Olympus). Nevertheless, Mally reasoned in effect that there must
be some mode of predication, some sense of the words ‘is’
and ‘has’ (German ‘ist’ and
‘hat’), for which it is true to say ‘Sherlock Holmes
is a detective’ and ‘Pegasus has wings’ (we wouldn't
understand the story and myth properly if we didn't imagine objects
that, in some sense, were instances of the properties in question).

So Mally informally introduced the notion ‘*x encodes
F*’ (German: *F determiniert x*) as a new mode of
predication that is more appropriate for the logical analysis of
sentences about fictions and other abstract objects. Whereas the real
detective Pinkerton exemplifies detectivehood
(‘*Dp*’), Sherlock Holmes encodes this property
(‘*hD*’). Mally's ideas can be extended to other
abstract objects, such as numbers, sets, possible worlds, etc.
Whereas we can identify and individuate concrete objects in terms of
their spatiotemporal location, we must identify and individuate
abstract objects in some other way, for abstract objects are not the
kind of thing that could have a location in spacetime. Encoding
provides the means of identifying and individuating abstract objects.
The properties that an abstract object encodes are part of its
intrinsic nature---they are even more essential to it than the
properties that such objects exemplify necessarily.

Further Explanation of the Distinction Underlying the Theory

To extend Mally's idea to its logical conclusion, therefore, we simply assert the following two principles:

- For each group of properties, there is an abstract object that encodes just the properties in that group.
- Abstract objects
*x*and*y*are identical if and only they (necessarily) encode the same properties.

Though the theory of abstract objects has been presented in books and
articles, there is one unpublished source in which all the theorems of
the theory are compiled in one place. This is the monograph entitled
*Principia Metaphysica*. It contains just the formal
machinery, axioms, and theorems of the theory with very little
accompanying explanation. It exists on-line in HTML, DVI (device
independent), compressed PS (PostScript), and compressed PDF (Adobe
Acrobat) file formats, and so can be examined with a graphical web
browser, DVI file previewer, PS printer, or Adobe Acrobat reader.
Since the manuscript contains little supporting explanation of the
formal machinery, it will appear highly technical. However, there is
help available for understanding the formal machinery, in the form of
a Tutorial (see below).

**Streaming Video Presentation of the Theory**

"Steps Toward a Computational Metaphysics",
by Edward N. Zalta and Branden Fitelson, *Computing and Philosophy
Conference*, Oregon State University, August 8, 2003

- HTML (2 KB) (version of July 10, 1996)
- PDF/Acrobat (900 KB) (version February 10, 1999)

**Tutorial on Principia Metaphysica**

This tutorial assumes either: (1) that you have a multi-window
graphical web browser that can display the HTML version of
*Principia Metaphysica* in one window and display the tutorial
in another other window, or (2) that your graphical web browser is
supported with a DVI, PS, or Acrobat previewer and that you are able
to flip back and forth between the (DVI, PS, or Acrobat) version of
*Principia Metaphysica* in your previewer and the tutorial in
your graphical web browser.

Tutorial

Copyright © 2004, by Edward N. Zalta. All rights reserved.