Alvin Plantinga’s claims revolve around individuals who argue against naturalist concepts such as the rejection of the existence of supernatural beings like God, but instead, support theories such as that of evolution.
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Plantinga claims that such individuals have a self-undermining set of beliefs. Plantinga uses various abbreviations to illustrate his claims, whereby naturalism is represented as N, the evolutionary theory as E, evolutionary naturalism as NE, and the reliability of cognitive faculties as R.
Plantinga’s arguments begin with a Probability Thesis, which is followed by the Defeater Thesis. The Probability Thesis states “the probability that R is true given the truth of N and E is either low or inscrutable” (Fales’ 434).
The Defeater Thesis, on the other hand, holds that “an evolutionary naturalist who is apprised of the Probability Thesis has a defeater for her belief in R” (Fales’ 434). This paper seeks to explain Plantinga’s Defeater Thesis and the basis for his beliefs, including his claim that the naturalist has a defeater for R and other beliefs.
The Probability Thesis holds that individuals are the product of an undirected evolutionary process, in the event that both N and E are true. However, the probability that a being with this sort of attribution would have reliable cognitive faculties is either low or inscrutable.
Hence, the assumption that the probability of individuals’ cognitive faculties are reliable given N and E are true is low or enigmatic (Fales’ 435).
Plantinga’s argument for the Defeater Thesis is based on the evaluation of instances whereby agents are observed to be contradicting their beliefs.
Plantinga also bases his arguments on the correlation between such individuals and evolutionary naturalists, who are facing a defeater for their belief in R, owing to their awareness of the Probability Thesis. Plantinga uses four analogical cases to argue for the Defeater Thesis.
These cases include the Widget Cases, the Freudian Theist Cases, the space Radio case, and the Brain-in-a-vat Case (Fitelson and Sober 119).
According to the Widget Cases, the individual is presented with two contradicting arguments about a situation that she is familiar with, causing her to doubt her beliefs. This is illustrated when the individual walks into a factory that appears to be manufacturing red-colored widgets.
However, the individual is informed by the shop superintendant that the widgets are red due to the effect of light on them, but majority of them are actually not red in color. Based on this revelation, the individual acknowledges that there is a low probability that the widgets are red in color.
However, the individual later encounters the vice-president of the production line, who claims that the superintendant cannot be trusted with the information provided earlier regarding the color of the widgets. This information causes the individual to have a dilemma about the color of the widgets.
Plantinga regards such a situation as causing the individual to be doubtful about her vision’s ability to provide her with accurate information regarding the color of the widgets, which causes the individual to have a defeater of color beliefs about widgets observed in an assembly line (Fitelson and Sober 120).
The other cases are also based on different situations that bring doubt to the individuals, causing them to question the rationale that made them belief or trust, in the first place. Based on this argument, a general principle of Low Reliability (LR) principle of defeat can be proposed in the form of:
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“S has a defeater for the belief p if, relative to all her evidence, S takes as low the probability that the source of p is reliable”.
The shortcoming with this LR principle is due to the fact that the individual in the widget’s case does not make the deduction that her perceptual faculties regarding the color of the widgets are unreliable under the circumstances of the case.
This implies that the LR principal falls short in explaining the reason for the defeater. In order to explain the defeater in the widget’s case, it can be assumed that the individual finds the rationale in the case.
For this intervention to pass as accurate, it is essential to identify the requirements of rationality that are relevant in the matter, as well as the kind of rationality that is raised in the case.
One of the requirements for the individual to identify the rationale behind her case can be identified by forming the belief that her “perceptual faculties concerning widgets are unreliable”.
However, this perspective is thought of as being too demanding in proving the rationale behind the case, as it would require the individual to condemn her perceptual faculties as unreliable.
She may also fail to acknowledge that her color detection faculties are unreliable in her situation, which is basically the reason why her defeater for color beliefs concerning the widgets manifests itself (Fitelson and Sober 121).
Another method of explaining the case of self-defeat in the scenario involves the use of internal and external rationality. Plantinga refers to “internal rationality as that which deals with maters “downstream” from experience, while external rationality deals with matters “upstream” from experience” (Fales’ 441).
The case of color belief pertains to irrationality that is downstream from experience, which requires elaboration on the basis of internal rationality (Fales’ 441). Plantinga argues that internal rationality can only occur if the agent possesses the required level of coherence.
As such, the belief that there is a defeater in the widget cases is due to the fact that the visitor would not satisfy the nominal level of coherence required for internal rationality in the event that she denied that the probability that her color-detecting faculties are reliable in the circumstances at hand is rather low.
Based on this argument, the Low Reliability (LR) principle can be re-written as:
“S has a defeater for the belief p if, relative to all of her evidence, S takes as low, or it would be internally irrational for S to deny as low, the probability that the source of p is reliable”.
The various factors that may have influenced the individual in the first case to believe regarding her cognitive faculty, which led to her belief in R, or the R-faculty, are influenced by the Unsubstantiated Source (US) principle of defeat, which holds that:
“S has a defeater for the belief p if, relative to all of her evidence, S takes as low or inscrutable, or it would be internally irrational for S to deny as low or inscrutable, the probability that the source of p is reliable”.
This implies that it would be internally irrational for her to deny that relative to all of her evidence, the probability that her R-faculty is reliable is either low or inscrutable. Based on the US principle, it is clear the individual has a defeater for her belief in R.
It is possible for someone to claim that it is internally irrational for the evolutionary naturalist, who is acquaint with the Probability Thesis, to deny that despite all the evidence, the probability that her cognitive faculties are reliable is low, based on the Attended No-reason (ANR) condition.
This principle concerns the level of coherence on the individual’s beliefs that is required for the person to be internally rational. The ANR condition holds that:
“if agent S’s attention is brought to bear on whether her belief B is formed in a warranted way, and it is internally irrational for her to accept any reason for thinking that B is warranted, then it is internally irrational for her to continue to believe B”.
This condition implies that the internal rationality of the agent’s acceptance of B can be influenced by the individual’s reflection on B, despite the agent’s acceptance of B prior to the reflection.
The variation is caused by the process of reflection, which causes the agent to consider whether B is warranted. The ANR principal proposes that it is internally irrational for the agent to continue to believe B after the revelation during her reflection (Fales’ 444).
The ANR principle explains how the evolutionary naturalist is supposed to proceed, from the acknowledgement of the Probability thesis, to the possession of a defeater for R. Reflection on the Probability Thesis is what causes the naturalist to focus on determining whether her belief in R is formed in a reasonable way.
In the event that there is no internal rationale to defend the belief, then it implies that the reflection on the Probability Thesis causes the evolutionary naturalist to have a defeater for her belief in R. As such the ANR principle forms a vital pillar in the support of Plantinga’s case against evolutionary naturalism (Fales’ 446).
Fales’, Evan. “Plantinga’s Case Against Naturalistic Epistemology.” Philosophy of Science 63 (3), (1996): 432-451. Print.
Fitelson, Branden and Elliott Sober. “Plantinga’s Probability Arguments Against Evolutionary Naturalism.” Pacific Philosophical Quarterly 79, (1998): 115-129. Print.