The Mind as Computer Metaphor: Benson and the Mistaken Application of Mental Steps to Software (Part 2)

Go to: Part 1, Part 2, Part 3, Part 4, Part 5

(This series of posts is based on an upcoming paper for the AIPLA Spring 2016 meeting.)


The fictional form of the mental steps doctrine arose in Benson, where the Court stated:

A digital computer, as distinguished from an analog computer, is that which operates on data expressed in digits, solving a problem by doing arithmetic as a person would do it by head and hand.1


the conversion of BCD numerals to pure binary numerals can be done mentally… can also be performed without a computer.2

Where did the Supreme Court come up with this principle that a digital computer solves problems the same way a person does? The Court cited Ronald Benrey, Understanding Digital Computers (1964) as support. First, it seems odd that a book titled Understanding Digital Computers (“UDC”), which would likely be directed to a technical discussion of the operation of digital computers, would make such an authoritative-sounding statement at a time when science had little real insight into how the human brain actually performs calculations. Second, the citation to UDC is illuminating but not sufficient, since clearly the Supreme Court did not do its own research to source this statement.

The explanation for the latter problem is that this principle was argued by the Solicitor General, based on a partial quotation from UDC:

A digital computer solves a problem by actually doing arithmetic in much the same way a person would by hand.3

The Solicitor General went on to argue that a computer performs essentially mental steps when performing calculations because “the conversion of BCD numerals to pure binary numerals can be accomplished by a conventional series of mental steps.”4 While the Solicitor General’s brief acknowledged that “the computer operates by physical equivalents of logical functions,” the Solicitor General nonetheless maintained that “the functions themselves are the same procedures which a human being would perform in working the same computation, but reduced to the physical characteristics of the device.”5 These two statements of procedural equivalence became the basis on which the Supreme Court transformed the mental steps doctrine from the factual form to its fictional one and applied it to computer-implemented inventions.

But that leaves the question of whether UDC actually made this rather bold assertion about the procedural equivalence of brains and computers. It turns out that it did not.

A careful reading of UDC shows that to support its argument that computers use the same procedures as humans, the Solicitor General took the various statements out of context.6 As author Ronald Benrey explains in his introduction to UDC, in 1964 “advances in electronic digital computer technology [had] made possible many spectacular scientific achievements that would have seemed like ‘science fiction’ three or four decades ago,” and computers were “generally pictured as incredibly complex electronic machines, aglow with flashing lights.”7 Benrey’s goal as a writer was to demystify computers and clearly explain that they “owe many of their capabilities to their inherent simplicity.”8 His book was not intended for scholars, but “for the person who wants more than a “cocktail party conversation” familiarity with digital computers, but who does not have the background or desire to delve into a rigorous consideration of electronic digital computer design techniques.”9

In the early 1960s, many hobbyists were familiar with analog computers, which had been in use for many years. Thus, before delving into the details of the structure of digital computers, UDC included a short section labeled What does “digital” mean? to distinguish between analog and digital computers. This is the section which the Solicitor General selectively quoted, and thus it is reproduced here in its entirety. The portion quoted by the Solicitor General is shown in italics:

The “digital” in digital computer tells us a lot about how these devices calculate. As we have said, input numbers are fed into a digital computer and output numbers are taken out. But what happens inside?

“Digital” describes any calculating mechanism that represents quantity with integers as it calculates. Another way of saying the same thing is that a digital computer solves a problem by actually doing arithmetic, in much the same way a person would “by hand.”

If you were to look inside a digital computer as it is performing a calculation (we will in later chapters) you would see different numbers represented by the mechanism at various times: At the start of the problem, the input numbers would be “visible.” Then, as the calculation goes on, “intermediate” results would appear. Finally, the answer would pop into view, just before it is sent out through the output. In effect, the computer is “writing the numbers down” as it does the arithmetic.

Notice that “digital” can be used to describe any calculating device that represents quantity in this fashion. Desk calculators, cash registers, abacuses and most mechanical counters, such as odometers, meet this requirement. These devices are actually mechanical digital computers. The abacus represents numbers with wooden beads, the others use gears or notched wheels.10

As is clear from the entire context of this section, UDC here explained that digital computers operate on digits—representations of discrete numbers. UDC provided additional examples to illustrate the concept, noting that many types of calculating devices familiar to 1960s readers can be considered digital: desk calculators, cash registers, abacuses, and even odometers in automobiles. Later on, Benrey returned to the idea that devices that manipulate numbers can be considered digital, writing, “We learned in Chapter 1 that digital mechanisms actually represent within themselves, the numbers being manipulated. Pascal’s adding machine, for example, represented the numbers with notched wheels. Each wheel had ten notches—one notch for each decimal digit.”11 Thus, it is clear from context that Benrey’s statement was as part of a larger discussion that related the meaning of digital—contrasted with analog—computation to something Benrey’s reader were familiar with—doing arithmetic. It was not intended as a statement of scientific fact that computers operate like human brains.

Moreover, as a full reading of the third paragraph makes clear, Benrey used a simple analogy—arithmetic done with pencil and paper—to help lay readers understand this foundational concept. Obviously one cannot “look inside” a computer to “see” actual numbers “pop into view”—this is simply a useful metaphor—nor does the computer “write down” anything on paper. When UDC was published in 1964, most people performed simple arithmetic using pencil and paper, and so Benrey used the pencil-and-paper analogy since it would have been instantly understood by every reader. That made it an effective and obvious figure of speech to help readers grasp an essential difference between analog and digital computers—but it was never intended as a scientific statement.

Most importantly, Benrey indeed took pains to point out that computers operated differently from human minds. In other portions not cited by the Solicitor General, Benrey expressly distinguished computers from human minds. In his introduction, Benrey lamented that “newspapers are forever reporting the latest feat performed by an electronic brain. As a result amazing intellectual powers and super-human thinking abilities have been attributed to digital computers.”12 Benrey then stated that “digital computers cannot ‘think,’ and as we shall see, they are not as complicated as most people believe. In fact, computers owe many of their capabilities to their inherent simplicity.”13 Benrey went on to explain that “No computer ‘thinks for itself’; it only operates at high speed according to the instructions it has received.”14

In summary then, UDC provided no support—indeed precisely contradicted—the proposition for which the Solicitor General cited it, and upon which the Supreme Court relied when it applied the mental steps doctrine to Benson’s claims.


1 409 U.S. at 65 n.3, citing Benrey, Understanding Digital Computers, New York, John Rider Pub. Inc. (1964) p. 4.

2 Id. at 67.

3 Brief of Solicitor General, Gottschalk v. Benson, 1972 WL 137527 *4 (U.S.) (hereinafter “Solicitor General Brief”), citing UDC, at 4.

4 Id. at *12.

5 Id. *7 (emphasis added).

6 Significant portions of this section are based upon the Brief of Ronald Benrey as Amicus Curiae, Alice Corp. v. CLS International, 573 U.S. ___ (2014) No. 13-298, which I co-authored, and personal communications with Mr. Benrey.

7 UDC at 2.

8 Id. at 3

9 Id.

10 Id., at 4-5. (emphasis added).

11 Id. at 28.

12 Id at 2. Given the availability of academic textbooks on digital computers available in 1972, it’s unclear why the Solicitor General relied upon a hobbyist book from 1964 to support its argument.

13 Id. at 3.

14 Id.

*The perspectives expressed in the Bilski Blog, as well as in various sources cited therein from time to time, are those of the respective authors and do not necessarily represent the views of Fenwick & West LLP or its clients.