Theo Todman's Web Page - Notes Pages

Personal Identity

Similarity

(Text as at 06/07/2023 00:43:12)

Plug Note¹

• Thesis Text:
  1. The logic of similarity, like the logic of identity², is a prerequisite for understanding continuity³ and change⁴.
  2. It is important to distinguish identity from exact similarity, as in the case of "identical" twins" which are not identical in the strict logical sense.
  3. Some initial thoughts:-
     1. “Exact Similarity” is an equivalence relation in that it is reflexive, symmetric and transitive.
     2. “Similarity” is less obviously an equivalence relation – however it is defined – because the transitivity relation may be deemed to fail.
     3. “Identical twins” – despite the suggestion above – are not even “exactly similar” in the strict sense, as it’s only genetically that they are exactly similar. In principle, each set of chromosomes in either twin is exactly similar to any other. And, I suppose, we could say that as their genomes are abstract objects, they are numerically identical. But the bodies and minds of identical twins – while “similar”, barring accidents, are not “exactly similar”, other than immediately after birth (and then only if we’re lucky).
     4. “Exactly similar” individuals would seem to have all non-relational properties in common. To make the term useful in practical life, we might have to allow some latitude. If I want my television replaced by an “exactly similar” one, I want one that’s how the one I bought ought to have been without whatever defects are inducing me to return it. Nor may I care for trivial differences in weight, surface marks and the like.
     5. “Similarity” applies to particular properties of things (“wearing similar ties”) or to individuals in their entirety (as “identical twins”).
        

References

• Relevant Works cited above: No items to list.
• For a Page of Links⁵ to this Note, Click here. A huge list, so no possibility of an updating run, but very useful to cherry-pick from.
• Works on this topic that I’ve actually read⁶, include₇ the following:-
  • Aeon:
    1. "Suchow (Jordan) - Haven’t we met before? On doppelgängers and perception", 2018, External Link, Internal PDF Link
  • General:
    1. "Hirsch (Eli) - A Sense of Unity", 1982
    2. "Hirsch (Eli) - Natural Kinds and Natural Units", 1982
    3. "Kagan (Shelly) - What matters (continued); The nature of death, Part I", 2007, External Link
    4. "Olson (Eric) - The Human Animal: Introduction", 1999
    5. "Parfit (Derek) - What We Believe Ourselves To Be", 1986, Write-Up Note⁸
    6. "Shoemaker (David) - Personal Identity and Immortality", 2009
• A further reading list might start with:-
  • General:
    1. "Brennan (Andrew) - Similarity and Affordance", 1988
    2. "Deutsch (Harry) - Identity and General Similarity", 1998, Internal PDF Link
    3. "Fodor (Jerry) - Similarity", 1998, No Abstract
    4. "Gratton-Guiness (I.) - Structural Similarity or Structuralism? Comments on Priest's Analysis of the Paradoxes of Self-Reference", 1998
    5. "Heil (John) - Imperfect Similarity", 2003
    6. "Hirsch (Eli) - Projectibility and Strange Languages", 1993
    7. "Hirsch (Eli) - Similarity and Natural Properties", 1993
    8. "Koslicki (Kathrin) - Constitution and Similarity", 2004, External Link, Internal PDF Link, Read = 6%
    9. "Martin (C.B.) - Identity and Exact Similarity", 1958, Internal PDF Link
    10. "Maurin (Anna-Sofia) - Same But Different", 2005, Internal PDF Link
    11. "Morreau (Michael) - It Simply Does Not Add Up: Trouble With Overall Similarity", 2010, Internal PDF Link
    12. "Nerlich (G.C.) - Sameness, Difference and Continuity", 1958, Internal PDF Link
    13. "Shoemaker (Sydney) - Phenomenal Similarity", 2003, No Abstract
    14. "Taylor (Barry) - Transworld Similarity and Transworld Belief", 2004, No Abstract
    15. "Vander Laan (David) - Counterpossibles and Similarity", 2004, No Abstract

  ---

• For a list of Works that have been considered, but have missed the cut for inclusion in this Section of my Thesis, see the following:-
  1. Read: No items to list.
  2. Further Reading: No items to list.
• This is mostly a place-holder⁹.

---

In-Page Footnotes:

Footnote 7:

• Most of these references touch on the topic of Similarity somewhat tangentially.

---

Table of the Previous 10 Versions of this Note:

Date	Length	Title
20/09/2022 11:24:00	3478	Similarity
01/05/2022 18:20:10	3097	Similarity
17/02/2021 18:50:24	3038	Similarity
31/05/2020 23:55:41	2683	Similarity
14/07/2019 18:05:46	609	Similarity
11/03/2018 20:19:41	1909	Similarity
18/12/2010 19:58:05	391	Similarity
26/11/2007 23:25:26	381	Similarity
10/11/2007 13:17:46	332	Similarity
12/08/2007 10:17:46	327	Similarity

---

Note last updated	Reading List for this Topic	Parent Topic
06/07/2023 00:43:12	Similarity	Logic of Identity

---

Summary of Notes Referenced by This Note

Awaiting Attention (Personal Identity)	Change	Continuity	Logic of Identity	Note Links Explanation
Parfit - What We Believe Ourselves To Be	Plug Note Apologia	Works Read - Explanation

To access information, click on one of the links in the table above.

---

Summary of Notes Citing This Note

Duplication	Personality	PID Note, Book & Paper Usage, 2, 3, 4, 5, 6, 7	Psychological Continuity - Forward	Teletransportation, 2
Thesis - Chapter 03 (What is a Person?)	Thesis - Chapter 04 (Basic Metaphysical Issues), 2, 3, 4, 5	Thesis - Chapter 10 (Thought Experiments), 2, 3	Thesis - Current Stance	Thesis - Personal Identity, 2, 3, 4, 5, 6
Website Generator Documentation - Functors, 2, 3, 4, 5, 6

To access information, click on one of the links in the table above.

---

Authors, Books & Papers Citing this Note

Author	Title	Medium	Extra Links	Read?
Baker (Lynne Rudder)	N/A	Author
Brennan (Andrew)	Similarity and Affordance	Paper
Deutsch (Harry)	Identity and General Similarity	Paper	2, 3, 4, 5
Doyle (Robert O.)	N/A	Author
Hirsch (Eli)	A Sense of Unity	Paper		Yes
Hirsch (Eli)	Natural Kinds and Natural Units	Paper		Yes
Hirsch (Eli)	Projectibility and Strange Languages	Paper	2, 3, 4, 5
Hirsch (Eli)	Similarity and Natural Properties	Paper
Honderich (Ted)	N/A	Author
Kagan (Shelly)	What matters (continued); The nature of death, Part I	Paper		Yes
Olson (Eric)	The Human Animal: Introduction	Paper	2	Yes
Parfit (Derek)	What We Believe Ourselves To Be	Paper		Yes
Shoemaker (David)	Personal Identity and Ethics - Introduction	Paper		Yes
Shoemaker (David)	Personal Identity and Immortality	Paper	2, 3, 4, 5, 6	Yes
Suchow (Jordan)	Haven’t we met before? On doppelgängers and perception	Paper	2, 3, 4, 5, 6	Yes
Tammet (Daniel)	N/A	Author	2, 3
Todman (Theo)	Thesis - Chapter 03 (What is a Person?)	Paper		Yes
Todman (Theo)	Thesis - Chapter 04 (Basic Metaphysical Issues)	Paper	2, 3, 4, 5	Yes
Todman (Theo)	Thesis - Chapter 10 (Thought Experiments)	Paper	2, 3	Yes
Todman (Theo)	Thesis - Current Position	Paper		Yes
Todman (Theo)	Thesis - Duplication	Paper		Yes
Todman (Theo)	Thesis - Personal Identity	Paper	2, 3, 4, 5, 6
Todman (Theo)	Thesis - Personality	Paper		Yes
Todman (Theo)	Thesis - Psychological Continuity - Forward	Paper		Yes
Todman (Theo)	Thesis - Teletransportation	Paper	2	Yes

---

References & Reading List

Author	Title	Medium	Source	Read?
Barbour (Ian)	Religion in an Age of Science	Book - By Subtopic (via Paper By Subtopic)	Barbour (Ian) - Religion in an Age of Science	No
Barbour (Ian)	Similarities and Differences	Paper - By Subtopic	Barbour - Religion in an Age of Science, 1990	No
Brennan (Andrew)	Conditions of Identity	Book - Cited (via Paper Cited)	Bibliographical details to be supplied	0%
Brennan (Andrew)	Similarity and Affordance	Paper - Cited	Brennan - Conditions of Identity, 1988, Chapter 7	No
Churchland (Paul)	Conceptual Similarity across Sensory and Neural Diversity: The Fodor-Lepore Challenge Answered	Paper - By Subtopic	Churchland & Churchland - On the Contrary: Critical Essays, 1987 - 1997	No
Churchland (Paul) & Churchland (Patricia)	On the Contrary: Critical Essays, 1987 - 1997	Book - By Subtopic (via Paper By Subtopic)	Churchland (Paul) & Churchland (Patricia) - On the Contrary: Critical Essays, 1987 - 1997	No
Fodor (Jerry)	Concepts - Where Cognitive Science Went Wrong	Book - By Subtopic (via Paper By Subtopic)	Fodor (Jerry) - Concepts - Where Cognitive Science Went Wrong	No
Fodor (Jerry)	Similarity	Paper - By Subtopic	Fodor - Concepts - Where Cognitive Science Went Wrong, Appendix 6A	No
Hains (Brigid) & Hains (Paul)	Aeon: Q-S	Book - Cited (via Paper Cited)	Bibliographical details to be supplied	29%
Heil (John)	Imperfect Similarity	Paper - By Subtopic	Heil - From an Ontological Point of View, 2003, Chapter 14	No
Jackson (Frank) & Priest (Graham), Eds.	Lewisian Themes: The Philosophy of David K. Lewis	Book - By Subtopic (via Paper By Subtopic)	Jackson (Frank) & Priest (Graham), Eds. - Lewisian Themes: The Philosophy of David K. Lewis	5%
Koslicki (Kathrin)	Constitution and Similarity	Paper - By Subtopic	Philosophical Studies, Vol. 117, No. 3 (Feb., 2004), pp. 327-364	6%
Maurin (Anna-Sofia)	Same But Different	Paper - By Subtopic	Metaphysica 6.1 (2005), pp. 129-148	No
Morreau (Michael)	It Simply Does Not Add Up: Trouble With Overall Similarity	Paper - By Subtopic	The Journal of Philosophy, Vol. 107, No. 9 (Sept. 2010), pp. 469-490	No
Shoemaker (David)	Personal Identity and Ethics - Introduction	Paper - Referencing	Shoemaker (David) - Personal Identity and Ethics: A Brief Introduction, 2009, Introduction	Yes
Shoemaker (David)	Personal Identity and Ethics: A Brief Introduction	Book - Referencing (via Paper Referencing)	Bibliographical details to be supplied	Yes
Shoemaker (Sydney)	Identity, Cause and Mind	Book - By Subtopic (via Paper By Subtopic)	Shoemaker (Sydney) - Identity, Cause and Mind	5%
Shoemaker (Sydney)	Phenomenal Similarity	Paper - By Subtopic	Shoemaker - Identity, Cause and Mind	No
Suchow (Jordan)	Haven’t we met before? On doppelgängers and perception	Paper - Cited	Aeon, 09 May, 2018	Yes
Todman (Theo)	Thesis - Similarity	Paper - By Subtopic		Yes
Vander Laan (David)	Counterpossibles and Similarity	Paper - By Subtopic	Jackson - Lewisian Themes: The Philosophy of David K. Lewis, Chapter 20	No

---

Text Colour Conventions

1. Blue: Text by me; © Theo Todman, 2025

---

© Theo Todman, June 2007 - May 2025.	Please address any comments on this page to theo@theotodman.com.	File output: 03/05/2025 12:28:10 Website Maintenance Dashboard
Return to Top of this Page	Return to Theo Todman's Philosophy Page	Return to Theo Todman's Home Page

---