In the interests of establishing a baseline we should first define Machine, according to the Merrium-Webster dictionary,
1a archaic: a constructed thing whether material or immaterialc archaic: a military engined: any of various apparatuses formerly used to produce stage effectse (1): an assemblage of parts that transmit forces, motion, and energy one to another in a predetermined manner (2): an instrument (as a lever) designed to transmit or modify the application of power, force, or motionf: a mechanically, electrically, or electronically operated device for performing a taskg: a coin-operated device <a cigarette machine> h: machinery —used with the or in plural2a: a living organism or one of its functional systemsb: one that resembles a machine (as in being methodical, tireless, or consistently productive) <a gifted publicist and quote machine— John Lancaster>c (1): a combination of persons acting together for a common end along with the agencies they use (2): a highly organized political group under the leadership of a boss or small clique3: a literary device or contrivance introduced for dramatic effect
The first thing that strikes me is the lack of specificity. Here we have a noun that can has many meanings and usages. However the word machine can also be a verb, again from Merrium-Webster,
transitive verb: to process by or as if by machine; especially: to reduce or finish by or as if by turning, shaping, planing, or milling by machine-operated tools
Both the noun, and the verb forms give us working baseline. Now in order to apply the definitions we must establish context.
1) We are not talking about anything "living"
2) We are not appealing to any metaphorical usage.
Now with our baseline and qualifiers I would like to take a closer look at the part of the definitions that we are interested in. Looking at the verb form and at the noun form 1(e)&1(f)
to process by or as if by machine; especially: to reduce or finish by or as if by turning, shaping, planing, or milling by machine-operated tools
e (1): an assemblage of parts that transmit forces, motion, and energy one to another in a predetermined manner (2): an instrument (as a lever) designed to transmit or modify the application of power, force, or motionf: a mechanically, electrically, or electronically operated device for performing a task
By putting these definitions together we arrive at,
an assemblage of parts that transmit forces, motion, and energy to either process or perform a task.
In the most technical terms a computer is still a machine. It makes use of energy to perform a self-referential task. This is why we refer to computers as "programmable." The tasks a computer performs are "within itself." It is this emergent property that I wish to examine most closely as it represents a complete break with the traditional definition of machine.
What is important to note here is that task is not fully concepted inside of machine's traditional definition. Up until the computer revolution this wouldn't have been an issue, as there was at the time no such "thing" as software.
The very emergent properties of software makes it innovative at its inception yet also calls into question the very identity of the processor itself. No other object can produce, or manipulate intangible self-reference. Now I can see some people here might insist that strictly mechanical processors (the Difference Engine) also have emergent properties. Yet this is not the case, as a change, even a subtle one, to the Difference Engine's hardware will result in a differing operation and function of its calculations.
So why shouldn't we class computers as "machines"? There is a subtle distinction when we look at the verb form of machine, it is a transitive verb. Thus we are to understand that a machine must have both a subject and a direct object. In the traditional understanding the Direct Object of a machine would be its work-piece, a tangible object.
Now in terms of computing the Direct Object of a processor is its software, yet software is itself responsible for the utility and operation of that same processor. Thus the only thing at can emerge from such an arrangement is "higher level" emergent operation. The "higher level" emergent operation will collapse if any of the "lower level" operations fail. This is classically represented by the Blue Screen of Death.
It is by the very propensity, and the mere possibility, for a collapse of emergent operation that we should seek to define the "computer" strictly as a "computer" and not as sub-category of machine. Indeed the Hacktivists are right to point out that we have yet to come to terms with such devices but by calling them "machines" we confuse ourselves into thinking that speech, text, pictures and video are actual objects of industry. When instead they are themselves merely human-emergent additions secondary to the physical process of tool-making which is used to perpetuate our species survival.
Computers are only Computers.