Functionalism, Identity Theory & Computational Models of Mind
Folk Psychology
Folk psychology explains the behavior of agents based on their mental states. It is the common-sense framework used to understand and predict behavior. Fodor defends folk psychology, offering reasons such as:
- It is highly successful in predicting behavior based on attributed intentions, beliefs, and desires.
- It explains how beliefs and desires interact causally to produce behavior.
- It posits that behavior results from a causal chain of mental events.
Turing Machines Explained
A Turing machine is an idealized theoretical model of computation. It operates algorithmically with key aspects including:
- An unlimited memory (represented as an infinite tape).
- Deterministic, error-free operation according to a set of rules.
Turing’s Theses and Computationalism
Turing’s work has significant implications for the philosophy of mind, particularly regarding computational theories.
Church-Turing Thesis
This thesis states that every effectively calculable function can be computed by a Turing machine (or an equivalent algorithmic process).
Key Definitions
- Algorithm: A finite set of well-defined, step-by-step rules applied mechanically to solve a problem or perform a computation.
- Computation: A process involving the manipulation of symbols according to defined rules.
Functionalism in Philosophy of Mind
Functionalism is an approach within the philosophy of mind aimed at understanding and classifying mental states. A central premise is that mental states are defined by their causal roles—their inputs, outputs, and relationships to other mental states—rather than their underlying physical or chemical composition. This allows mental states to be distinguished from the specific physical level implementing them.
Functionalism and Folk Psychology
Functionalism often interprets folk psychological concepts like beliefs and desires (propositional attitudes) as functional states. To explain an agent’s behavior, we refer to their beliefs and desires, understood in terms of their functional roles.
Mental States as Computational States
Functionalism, particularly machine-state functionalism, proposes identifying mental states with computational states within a system (analogous to states in a Turing machine). Consequently, a mental state isn’t tied to a specific physical state but represents a functional role that could, in principle, be realized by different physical systems (multiple realizability).
Mind-Brain Identity Theory
Proponents of the mind-brain identity theory argue that mental states and processes are identical to states and processes of the brain. Mental events are considered nothing more than physical brain events. Therefore, an individual cannot experience a specific mental event without a corresponding, specific neural circuit being active.
Philosophers supporting this theory typically accept type-physicalism, often with a reductionist view. They explore the possibility of reducing psychology to biology, suggesting that mental processes and states can ultimately be described by biological laws governing neural activity. Adherents to the identity theory are physicalists.
Logical Criticisms of Identity Theory
From a logical standpoint, strict identity is governed by Leibniz’s Law (the indiscernibility of identicals). This law states that if X and Y are strictly identical, they must share all the same properties. The criticism argues that mental states possess properties (like subjective quality or intentionality) that physical brain states seemingly lack. If a mental state has a property that its supposed identical brain state does not, then, according to Leibniz’s Law, they cannot be identical.
Metaphysical Criticisms: Multiple Realizability
A key metaphysical argument against identity theory stems from the concept of multiple realizability. It suggests that mental states are not identical to specific physical brain states because the same type of mental state can be realized or instantiated by different physical states. For example, the mental state of ‘pain’ might be realized by different neural structures in humans, octopuses, or hypothetical aliens. It is argued that two subjects can be in the same type of mental state even if their underlying brain states differ significantly. Type-identity theory struggles with this, as it implies that a specific mental state type must always correspond to the exact same physical state type, contradicting multiple realizability.
Classical vs. Connectionist Models
Computational models of the mind differ in their approach:
Classical Computational Models
These models view cognition as computation involving the manipulation of symbols according to explicit rules, similar to a traditional computer program or a Turing machine. Mental representations are symbolic structures.
Connectionist Models
Also known as Parallel Distributed Processing (PDP) models, these systems are inspired by the structure and function of the brain. They typically involve networks of simple processing units (‘neurons’). Information is represented in the pattern of connections (weights) and activation levels across the network, rather than as explicit symbols.