What do these years mean?

Question

I am currently reading The Limits of Realism by Tim Button. I'm having trouble understanding the convention of reference that he is using. On page 7, he writes the following:

That picture is of reasoning from a 'God's Eye point of view'.¹

Then at the bottom of the page, the following is written:

¹Putnam (1980a: 100; 1981c: 49; see also 1982a: 38; 1983a: x, xviii).

What do these years mean? I've looked at the bibliography, but I can't find sources corresponding to these years and the author. Here's the first two pages of the bibliography.

Answer 1

This answer merely adds detail to the answer given by @Allure.

In his book, Button uses a referencing system that seems to be somewhat non-standard. He combines a footnote style of referencing (with footnote numbers in each chapter being separately numbered from '1') with an author-date system. The superscript after the word view in the text indicates, as you have correctly shown, that there is a similarly numbered footnote at the bottom of the page.

The referencing system at the bottom of the page is an author-date system exactly as @Allure has indicated. In the 2013 edition (i.e., 1st edition) of Button's book (ISBN 978–0–19–967217–2) the sentence you have quoted appears on page 7. The bibliography for the book commences on page 245 and commencing on page 253 is a list of works by H. Putnam. If you look through that list, you will find two works with a 1980 publication date, one listed as 1980a, the other as 1980b; the work listed as 1980a is entitled How to be an Internal Realist and a Transcendental Realist (at the same time).

Answer 2

Most likely, Putnam has written multiple works which are all being cited. There are four of them, written in different years (1980, 1981, 1982, and 1983), and the citation gives more details on where to find the relevant information in all four of those sources.