I came across a striking passage tonight while I was leafing through The Elements of Philosophy, one of the texts for my class in Natural Philosophy. Pilate famously said to Christ, "What is Truth?", and when I read this all I could think was, "well that's settled!" More seriously, this is a nice summary of exactly what it means to say "this is true".
The term truth (14:327a) means in general some kind of agreement between thought and its object, between knowledge and that which is known. It is sometimes applied to things, and a thing is said to be true in the sense of ontological truth [§32.4]. In reference to speech, truth is called veracity or truthfulness [§14:335d], and is present when a person expresses what is in his mind. But the primary meaning of the word refers to the truth of the intellect, the truth of thought as opposed to the derived notions of truth of being and truth of speech. In this sense truth is a property of intellectual knowledge and is defined as the adequation of intellect and thing.
William A. Wallace, O.P. The Elements of Philosophy §39.1
Cross-posted to Dead Philosophers Society