Schlick's (1936) different definitions of the verificationist conception of meaning are strictly inconsistent. 

The meaning of a proposition is the method of its verification. (Schlick 1936, 341) [This is a variant of a verificationist conception of meaning.]

[W]henever we ask about a sentence, 'What does it mean?', what we expect is instruction as to the circumstances in which the sentence is to be used. (Schlick 1936, 341) [This is a kind of 'use theory' of meaning.]

[Whenever we ask about a sentence, 'What does it mean?'] we want a description of' the conditions under which the sentence will form a true proposition, and of those which will make it false. (Schlick 1936, 341) [This is a 'truth-conditional' conception of meaning.]

xxxxxxx.

Apparently, Schlick confuses conditions of verification (conditions, under which a certain proposition is verified) with truth conditions (conditions, under which a given proposition is true). The first and the third statement are clearly logically incompatible. Furthermore, the second statement is incompatible with either of these; to see this you need only appreciate that you can surely give circumstances in which 'Are you completely mad?!' is to be used, but cannot give either truth-conditions or conditions of verification of this expression.

Notice also that, on a natural and innocuous reading, Schlick identifies meaning with (a) a certain method, with (b) certain circumstances, and with (c) certain conditions. Clearly, these identifications classify meaning within distinct categories; accordingly, if one of these suggestions is accurate (which is far from clear anyway), the remaining two will appear to be based on category mistakes.