A priori it could be assumed that students and aficionados of memory will benefit from contemplating the concept of 'a priori'. Before defending the aforesaid statement, however, a brief clarification of the different meanings and uses of'a priori' is appropriate.
Prior to the eighteenth century, the pair of terms 'a priori'/'a posteriori' (Latin for 'from what is earlier'/'for what comes after') was used to distinguish between modes of reasoning: 'The mind can discover and understand the truth ... by demonstration. When the mind reasons from causes to effects, the demonstration is called a priori; when from effects to causes, the demonstration is called a posteriori' (Arnauld 1662). Only later were these nonidentical terminological-twins used to refer to types of knowledge: knowledge independent of experience is 'a priori', that which is grounded in experience is 'a posteriori' (Kant 1781). Traditionally since then, the pair 'a priori'/'a posteriori' is associated in the philosophical discourse with two other pairs of opposites: 'analytic' vs. 'synthetic', and 'necessary' vs. 'contingent' (Moser 1987; Grayling 1997). A statement is 'analytic' if its truth value can be determined by understanding the concepts or terms contained in it, whereas it is 'synthetic' if in order to determine its truth value we must know how the concepts or terms involved relate to other constituents of the world. Hence, adapting a commonly used illustration, 'singles are unmarried' is analytic, because 'single' is 'unmarried', whereas 'singles are happy' is synthetic, because it is not evident from 'singles' how their mood should be (the latter statement also demonstrates that some kinds of truth are "context specific or in the eye of the beholder, but this is another story). In formal terms, an analytic statement is thus a tautology, and its truth value follows necessarily. The latter property leads us to the third related pair of opposites: 'necessary' vs. 'contingent'. 'Necessary' refers to statements that must be either true or false due to what they state, whereas in 'contingent' statements the truth value is contingent upon other occurrences or relationships in the world. Discussion of the 'necessary'/'contingent' pair is within the realm of metaphysics, the 'analytic'/'synthetic' pair deprives logicians of sound sleep, whereas 'a priori'/ 'a posteriori' is within the domain of epistemology (the science of knowledge) (Moser 1987; Grayling 1997; Bealer 1999).
It is the epistemological connotation of'a priori' that interests us here. Furthermore, we focus on only a limited portion of the universe: the individual organism, its brain, behaviour, and memory. Construing 'experience' in definition 1 as any behavioural or physiological experience of the individual, leaves only one source of a priori knowledge in the individual brain: the genetic material. Genes carry information about a variety of behavioural capabilities and capacities ("neurogenetics). This information is hence 'innate'.1 As far as the individual is concerned, this is bona fide a-priori knowledge. For the species it is not, because the knowledge is supposed to have been acquired over time, a posteriori, by natural selection in evolution. However, it is also useful to consider as 'a priori' that knowledge that cannot be explained solely by the individual's experience. Such knowledge is generated by "developmental processes, via the interaction of genes and environment in prenatal and early postnatal periods. It is also produced throughout life by the endogenous activity of the brain, which depends on the processing of both innate and acquired knowledge. Definition 2 is colloquial: according to it, 'experience' is 'experience at the present time', e.g. while on a learning task. Hence according to this liberal interpretation any experience provides a priori knowledge for future experiences. This connotation of a priori gravitates toward the trivial, and will not be further discussed here.
A priori knowledge of both innate and postnatal origin fulfils multiple roles in behaviour and behavioural "plasticity:
1. Innate knowledge underlies reflexes and predetermined behavioural routines such as used in feeding, mating, fighting, and fleeing (Lorenz 1981; Dudai 1989). These behaviours vary in their dependency on postnatal experience. Some are essentially independent of experience, although they still may be perfected or modified by it, e.g. a-type "classical conditioning. Other behaviours require experience for maturation, fine tuning, and optimal "performance. This experience may have to be provided during a restricted 'sensitive period' in life, as in "imprinting (Lorenz 1981) and "birdsong (Nelson and Marler 1994). Another, more general type of 'prepared' or 'constrained learning', in which the type of associations, but not their actual content, is constrained a priori, is "conditioned taste aversion: we are inclined a priori to associate the taste of foodstuff with subsequent visceral malaise but not with a painful blow to the skin (Garcia et al. 1968). Admittedly, most philosophers would not like the use of the term 'knowledge' in the context of such 'simple' behaviours: 'No philosopher will be disturbed if Lorenz tells him that young geese follow the farmer around without previous conditioning or training. If Lorenz were to add that the young goose knows that it should follow the farmer, or that the farmer is a friend, philosophical ears would be pricked' (Cooper 1972). However, first of all, 'knowledge' is here used in its most "reductive connotation, not necessarily involving "conscious awareness ("internal representation); second, irrespective of the status of philosophical ears, the question whether animals are 'consciously aware' or not is not yet settled ("declarative memory).
2. Innate knowledge underlies capacities and operational rules of higher brain faculties such as language and mathematical abstraction in humans ('the speaker of a language knows a great deal that he has not learned', Chomsky (1966); compare Socrates on geometry: 'Try to discover by recollection what you do not know, or rather what you do not remember', Plato, Meno 86b).
3. Perhaps most intriguing is the notion that a priori knowledge that draws from a combination of innate and acquired resources permits our brain to anticipate the world on a momentary basis (e.g. Anokhin 1974). This issue relates to one of the most profound problems in the neurosciences and the philosophy of mind: the relationships of internal representations to the outside world. Let us consider two basic possibilities. One is that input from the world somehow instructs the brain to generate specific internal representations of reality. This type of process does not necessitate a priori knowledge, although it may still benefit from it. The other possibility is that the world somehow selects representations among 'pre-representations', which are generated endogenously in the brain (Young 1979; Heidmann etal. 1984; Dudai 1989; Edelman 1993; "stimulus). The 'selectionist' view has a Darwinian flavour, and likens the ontogenesis of our mind to the phylogenesis of our species. According to this view, the mammalian brain is not a passive observer but rather an active agent that anticipates the immediate future ("planning), and toward that end keeps itself busy by generating internal "models of reality. The postulated rules that guide 'the survival of the fittest internal models' may take into account predictions based on both innate knowledge and accumulated experience, and congruency with the on-line demands of the real world as conveyed by the senses. Such capacity is hence expected to be subserved in every individual of the species by two tiers of a priori knowledge. First there are the species-specific innate components responsible for much of the rules and the hardware, namely the computations, "algorithms and neuronal devices that enable the brain to generate and stabilize the aforementioned pre-representations
("level). Then there is the ongoing flux of the short-lived pre-representations themselves, which are unique to each individual of the species, and could be regarded as flashes of subjective knowledge preceding "perception and the "acquisition of memories. In this case, the past literally chases the present, and 'a priori' may refer to a time-scale of seconds only. Still, this is 'a priori', because at least part of the information is not derived from actual experience in the outside world.
The 'selectionist' hypothesis hence implies that we continuously anticipate the world and generate approximate models of it, and that both endogenous and exogenous information combine to represent reality (e.g. Arieli et al. 1996). This raises the question how faithful to reality are our internal representations ("false memory, "real-life memory). We may assume that in the course of evolution, our ability to model the world, learn about it, and interact with it has been shaped to reach a reasonable correspondence of the internal models to reality. The fact that organisms succeed in negotiating with an ever changing milieu attests to that. But not all our memory "systems ("taxonomy) have been subjected to the same selective pressures, such as the pressure for improved precision and detail. Hence, whether a specific type of memory, such as "declarative, is inherently faithful to reality or not, is itself a priori influenced by evolutionary forces.
Last, we should not "forget that in daily life we are all constrained by a priori assumptions that could "bias our personal (or "cultural) attitude toward events, facts, and disciplines. The attitude toward 'memory' is not expected to be an exception.
Selected associations: Acquisition, Bias, Development, Palimpsest
'For *classic philosophical attitudes to innate knowledge in general, see Locke (1690) and Leibniz (1704).
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