To believe a proposition, say corn flakes have health benefits, is to accept it to be true. However, the question of belief is valid only for those propositions that are understandable. An understandable proposition is one that is expressed using correct grammar and known words.
The dominant view in the scientific community on how human mind believes or disbelieves an understandable proposition is the Cartesian hypothesis, propounded by the seventeenth-century philosopher René Descartes. He said that when an understandable proposition is presented to a human mind, the comprehension of its content happens automatically and passively; however, the assessment of the truth-value of that proposition is a later and deliberate act, the result of which is either belief or disbelief. Thus, this view holds that belief or disbelief in a comprehended proposition is created by rational assessment, and till such an assessment is made, the intellect neither affirms nor denies a comprehended proposition. It also suggests that the mental effort required to create belief and disbelief is the same: the effort required to assess the comprehended proposition.
In contrast, Descartes's near-contemporary Baruch Spinoza suggested that comprehension of and belief in an understandable proposition happen together, automatically and passively; he said that it is not possible to understand a proposition without, at least temporarily, accepting it to be true. On later, willful assessment, if one judges the believed proposition to be false, it may be unaccepted (disbelieved), and if judged to be true, one may continue to believe in it. Thus, as per the Spinozan hypothesis, the default setting of the human mind is to believe every understandable proposition that is presented to it; disbelief is possible but it comes – if it comes at all – from effortful, deliberate assessment done after the initial comprehension-belief.
Both hypotheses continue to have their proponents and opponents. It is, however, a common observation that doubt, suspension of judgment and disbelief are mentally taxing tasks while we naturally – effortlessly – accept and believe most of what we see, hear and read. Research has proved that we systematically err on the side of believing too much, as opposed to rejecting too much. This inherent credulity of the human mind is, in fact, the founding axiom of the fields of advertising and propaganda.
Adapted from a research paper by Professor Daniel Gilbert