There is a widely held view that the expressions ‘necessary truth’, ‘a priori truth’ and ‘analytic truth’ either express the same concept or, at least, refer to all and only the same items. Philosophers who hold this view, and who are sometimes described as ‘empiricists’, often draw the conclusion that the truths of logic and mathematics, if necessary, are also a priori and are, in some important sense, empty or not about the world. The subject matter of these disciplines, then, is said to differ in a philosophically important way from that of the empirical sciences, such as physics or chemistry. Rationalists, in contrast, have traditionally held that some a priori truths, either of logic or mathematics (or of some other area), are synthetic and, hence, non-analytic: i.e., there are synthetic a priori truths.

This paper discusses several philosophical problems with the use of randomized clinical trials (RCTs) in psychotherapy outcome research. The problems include: the impermanence problem, the identification problem, and idiographic problems. The paper concludes with an assessment of the overall case for and against the use of RCTs in psychotherapy outcome research.

In this commentary, I agree with Chow's treatment of null hypothesis significance testing as a noninferential procedure. However, I dispute his reconstruction of the logic of theory corroboration. I also challenge recent criticisms of NHSTP based on power analysis and meta-analysis.

John Greenwood (this issue) claims that neglect of an important methodological distinction has contributed directly to the “epistemic impoverishment” of empirical studies of all forms of professional psychotherapy. I challenge this claim, as well as other important claims he makes about the efficacy of psychoanalysis and other forms of psychotherapy.

Poly(γ-benzyl-L-glutamate) (PBLG) derivatized at its N-terminus with lipoic acid, a disulfide-containing moiety, self-assembles on gold from helicogenic solvents to give a thin film with the polypeptide α-helices orientation distribution different from the planar orientation in the unlabeled, physisorbed PBLG films (control) and Langmuir-Blodgett monolayers. The SA films were studied by angle-dependent XPS, reflection-absorption FTIR spectroscopy, and ellipsometry. The IR dichroic properties of the amide I and amide II bands were used to infer the orientational distribution of the helices in the self-assembled film and lead to two extreme pictures of the helix axis distribution function: (a) random (hemispherical distribution) and (b) perfect order with a tilt of 53° from the surface normal. Additional characterization is necessary to differentiate between these two distributions.

It is customary to draw a distinction between statements unconfirmable in practice and statements unconfirmable in principle. It may be impossible, for example, to confirm the statement “The star most distant from us in the universe has recently doubled in size,” but this impossibility is not of a logical kind. We could conceive of tests which would either confirm or disconfirm the statement, even if in fact we cannot carry them out. In contrast, the statement ‘Everything has recently doubled in size’ cannot be confirmed for logical reasons, or so some philosophers have claimed. If everything were to double in size, including the very measuring rods used to detect expansions, it would be logically impossible, so the argument runs, to either confirm or disconfirm the above statement.