The first argument is made by neurosurgeon Michael Egnor in a June 2, 2017 blog post at evolutionnews.com entitled "Prairie Dogs Are Cute, But Can They Talk?" (see here). Egnor is responding to a recent article in The New York Times Magazine. In the article, a biologist who has studied prairie dogs for many years is quoted as saying that prairie dogs actually have language. Egnor responds that the "assertion that non-human animals [like prairie dogs] have language is... nonsense." He goes on to back up his opinion with the following argument.
According to Egnor, communication takes place via signs--"sounds or gestures or images that point to something beyond themselves." There are two types of signs--signals and designators. Egnor continues:
...Signals are “concrete” signs that point to things that are in proximity, either in location or in time. Pointing to a dog is a signal that young pre-verbal children often use. A cross or a Star of David on a house of worship is a signal. It identifies the place as a church or a synagogue. A traffic light is a signal — it uses colored lights to tell us to stop or go.
The key to a signal is that it points to particular proximate things, either objects or ideas. Signals are concrete, not abstract. The signal is connected in a physical way to that which is signifies. All animal communication is by signals. Note that signals can be complex, and animal communication can be complex. But animal communication is concrete, not abstract.
In contrast, Egnor says, designators are abstract by nature. They point to things or ideas in an abstract way. For example, the word cat is a designator for a particular animal. The word itself is merely "electrons on a screen or ink on paper," and "doesn't point in any direct or proximate way to any particular animal." When we read the word cat, there is usually no actual cat physically present or even present in our memory. In short, the word cat is "an abstract sign, and it is abstraction — the removal of the sign from any specific particular thing — that makes [it] a designator rather than a signal."
Egnor argues that the essential distinction of human language is that only it employs designators (words). Moreover, in human language words appear within a certain pattern (syntax). As he says:
...Words are arranged syntactically, to enhance meaning. Some words are nouns, which designate things, and some words are verbs, which designate change or states of being. Proper names designate particular things, and general names designate universals. You will notice that the structure of genuine language, as contrasted with a set of signals, has a metaphysical structure — it uses signs that point to particulars and universals and change and states of being. Signals lack this metaphysical structure.
In brief, animals cannot have language because they can only communicate using signals, not designators (words) as humans can.
The second argument as to why animals do not possess language is made by Christian philosopher J.P. Moreland in his book The Soul: How We Know It's Real and Why It Matters. For his part, Moreland makes a distinction between signs and symbols in his discussion of animal "language." He tells us:
...A sign is a sense-perceptible object, usually a shaped thing like the characters "BANANA" or a sound (the utterance of "BANANA"). Now if an animal...comes to experience repeatedly the simultaneous presence of a sign (the visual presentation of BANANA) and the presence of a real banana, a habitual association will be set up such that the animal will anticipate the sense perception of a real banana shortly after seeing this shape: BANANA. In the case of the animal, BANANA does not represent or mean a banana, so it is not a symbol. Rather BANANA is merely a certain geometrically perceived shape that comes to be associated with a banana in such a way that the latter is anticipated when the former is observed.
By contrast, real language requires symbols and not mere signs. When language users use the word banana, it is used to represent, mean, and refer to actual bananas. Now the evidence suggests that animals have certain abilities to manipulate and behaviorally respond to signs, but it is far from clear that they have a concept of symbols. (p. 144)
In short, for Moreland, animals do not have language because they are unable to use symbols.
These two arguments appear to be similar, but are not quite identical. For Egnor, animals use signals, which point to something proximate in place or time, while for Moreland, animals use signs, which are associated by experience with the perception of some object. However, Egnor's signals and Moreland's signs are similar in that they both involve the actual (or presumed) presence of the thing they point to. Moreover, Egnor and Moreland agree that what distinguishes human language from animal communication systems is the fact that human language alone uses words (designators for Egnor; symbols for Moreland), which are abstract/symbolic by nature.
To conclude, both Egnor and Moreland give compelling--though slightly different--philosophical arguments for the view that animals do not possess language. Nevertheless, the persistence of the belief that animals do have language demonstrates that some are determined to erase the distinctions between animals and humans regardless of the evidence to the contrary.
Image of prairie dogs from Wikimedia Commons