  Although the meaning of the word ‘intentionality’ in contemporary philosophy is related to the meanings of such words as ‘intension’ (or ‘intensionality’ with an s) and ‘intention,’ nonetheless it ought not to be confused with either of them. On the one hand, in contemporary English, ‘intensional’ and ‘intensionality’ mean ‘non-extensional’ and ‘non-extensionality,’ where both extensionality and intensionality are logical features of words and sentences. For example, ‘creature with a heart’ and ‘creature with a kidney’ have the same extension because they are true of the same individuals: all the creatures with a kidney are creatures with a heart. But the two expressions have different intensions because the word ‘heart’ does not have the same extension, let alone the same meaning, as the word ‘kidney.’ On the other hand, intention and intending are specific states of mind that, unlike beliefs, judgments, hopes, desires or fears, play a distinctive role in the etiology of actions.  By contrast, intentionality is a pervasive feature of many different mental states: beliefs, hopes, judgments, intentions, love and hatred all exhibit intentionality. In fact, Brentano held that intentionality is the hallmark of the mental: much of twentieth century philosophy of mind has been shaped by what, in this entry, will be referred to as “Brentano’s third thesis.” 