Usually, the specifications will say that they govern over the drawings- if they don't say, ask whoever wrote them. In reality, the plans tend to be right more often, as they are custom done for the job, and the specs tend to get printed out without being read.
The construction contract should detail the order of precedence for the construction documents. In contracts usually specs govern over drawings.
A problem can arise if there is a discreptancy within the governing document. In the event of an ambiguity, case law usually rules against the party that drafted the documents.
My understanding is that normally construction specs govern over drawings in the building industry and that plans govern over specs in the bridge industry.
The statement "unless specified on drawings" oftenly appears in the construction specs. I believe it's fair enough to conclude that drawings usually govern.
Most contracts (e.g., FIDIC) have in the general terms and conditions a listing (as dik intimated) of precedence. My previous job had, at No5 on the list the Specifications, No 6 was the Drawings and No. 7 was the BOQ. On the job I am currently on, the BOQ appears to have precedence over the specs and drawings.
Loui1 and Henri2... it has to be declared somewhere and that is usually in the contract... else, it's a matter for the lawyers to determine, and that may be based on common practice.
The general note and typical detail may have similar weight unless stipulated... in general, drawings/details of a larger scale have prescedent over drawings of a lesser scale... and catch my note about an ambiguity...
Many structural plans have a CYA general note similiar to: "if a discrecpancy arises within the plans or between the plans and specifications the most stringent provisions shall control" -now who decides what is most stringent etc...
