1. A term that tells us which individual is being talked about. (John Stuart Mill
   John Stuart Mill
   John Stuart Mill was a British philosopher, economist and civil servant. An influential contributor to social theory, political theory, and political economy, his conception of liberty justified the freedom of the individual in opposition to unlimited state control. He was a proponent of...
   
   , Arthur Prior
   Arthur Prior
   Arthur Norman Prior was a noted logician and philosopher. Prior founded tense logic, now also known as temporal logic, and made important contributions to intensional logic, particularly in Prior .-Biography:Prior was entirely educated in New Zealand, where he was fortunate to have come under the...
   
   , P. F. Strawson
   P. F. Strawson
   Sir Peter Frederick Strawson FBA was an English philosopher. He was the Waynflete Professor of Metaphysical Philosophy at the University of Oxford from 1968 to 1987. Before that he was appointed as a college lecturer at University College, Oxford in 1947 and became a tutorial fellow the...
   
   )
2. A term that is grammatically singular, i.e. a proper name
   Proper name
   "A proper name [is] a word that answers the purpose of showing what thing it is that we are talking about" writes John Stuart Mill in A System of Logic , "but not of telling anything about it"...
   
    (proprium nomen), a demonstrative pronoun (pronomen demonstrativum) or a demonstrative pronoun with a common name (cum termino communi). (William of Ockham
   William of Ockham
   William of Ockham was an English Franciscan friar and scholastic philosopher, who is believed to have been born in Ockham, a small village in Surrey. He is considered to be one of the major figures of medieval thought and was at the centre of the major intellectual and political controversies of...
   
   )
3. A term that is inherently about the object to which it applies or refers
   Reference
   Reference is derived from Middle English referren, from Middle French rèférer, from Latin referre, "to carry back", formed from the prefix re- and ferre, "to bear"...
   
   . (Gottlob Frege
   Gottlob Frege
   Friedrich Ludwig Gottlob Frege was a German mathematician, logician and philosopher. He is considered to be one of the founders of modern logic, and made major contributions to the foundations of mathematics. He is generally considered to be the father of analytic philosophy, for his writings on...
   
   )
4. A term that is true "in the same sense" of only one object. (Peter of Spain
   Peter of Spain
   Peter of Spain or, in Latin, Petrus Hispanus is the Mediaeval author of Tractatus, later known as Summulae logicales magistri Petri Hispani , a standard textbook on logic...
   
   )

Works cited

• Frege, G. (1892) "On Sense and Reference", originally published as " Über Sinn und Bedeutung" in Zeitschrift für Philosophie und philosophische Kritik, vol. 100, pp. 25-50. Transl. Geach & Black 56-78.
• Mill, J.S., A System of Logic, London 1908 (8th edition).
• Petrus Hispanus, Summulae Logicales, ed. I. M. Bochenski (Turin, 1947) – also quoted in Prior 1976
• Prior, A.N. The Doctrine of Propositions & Terms London 1976
• Strawson, P.F. "On Referring", Mind 1950 pp. 320-44.
• William of Ockham, Summa logicae
  Sum of Logic
  The Summa Logicae is a textbook on logic by William of Ockham. It was written around 1323.Systematically, it resembles other works of medieval logic, organised under the basic headings of the Aristotelian Predicables, Categories, terms, propositions, and syllogisms...
  
  Paris 1448, Bologna 1498, Venice 1508, Oxford 1675