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A POSTERIORI. Latin, “from later.” A
posteriori knowledge stems from experi-
ence or observation and so cannot be
known beforehand by pure reason or
conceptual analysis. We know a posteri-
ori, for example, that Socrates was exe-
cuted in 399 BCE. Some traditional
arguments for God’s existence such as the
teleological and design arguments are
developed a posteriori.

A PRIORI. Latin, “from earlier.” A pro-
position is known a priori when it is
known without employing empirical
observations or experience. Arguably, one
may know a priori that there cannot be
a square circle.

ABDUCTION. From the Latin ab + duc-
ere, meaning “to lead away.” Abductive
reasoning explains phenomena on the
grounds of prior probability or reason-
ability. For example, one might argue for
theism on the grounds that if theism is
true, it is more probable that there would
be an ordered cosmos with conscious,

valuable life, than if a non-theistic alter-

native is assumed to be true, such as

secular naturalism. Abductive reasoning

is most often employed in comparing a

limited number of alternative theories.

The earliest theistic design arguments in

English were abductive in structure as

opposed to inductive. Henry More rea-

soned that the cosmos was akin to what

appears to be language; if we assume

there is a creator, the cosmos is (as it

seems) intelligible, whereas it does not

seem intelligible if there is no creator.

ABELARD, PETER (1079–1142). Abelard

is best known for his metaphysics, ethics,

and understanding of atonement. In

metaphysics, he adopted a form of con-

ceptualism, a position midway between

Platonism and nominalism. In ethics, he

greatly stressed the role of intentions

and desires. He thereby put stress on the

moral relevance of our interior life. If Abe-

lard is correct, then an ethic that focuses

exclusively on external action is inade-

quate. In theology, he is attributed with

what is sometimes called a subjective