FTD is a complex, multidimensional syndrome characterized by deficiencies in the logical organizing of thought needed to achieve goals. FTD can be subdivided into clusters of positive and negative symptoms, as well as objective versus subjective symptoms. Within the scale of positive and negative symptoms they have been grouped into positive formal thought disorder (posFTD) and negative formal thought disorder (negFTD). Positive subtypes were those of pressure of speech, tangentiality, derailment, incoherence, and illogicality. Negative subtypes were those of poverty of speech and poverty of content. The two groups were posited to be at either end of a spectrum of normal speech. However, later studies showed these to be poorly correlated. A comprehensive measure of formal thought disorder is the "Thought and Language Disorder (TALD) Scale".