(a) Think first: and/or

Do not ever write and/or. It is the metaphor for laziness and vacuous writing. For clarity in bold print: never write and/or.

For several reasons, there is no need to write the ‘slashed combo’, not even for simplification or keeping the text short. First, the drafter imposes on each of the readers of the contract the necessity to take over the thinking work, which the drafter failed to do. Secondly, the simplification is that the actual meaning of and/or (namely the choice between either A or B or A or B or both) is somehow left to the reader. Thereby, it allows the reader the possibility to cherry pick either and or or whichever is the most favourable interpretation.
Thirdly, using and/or completely fails to meet the drafting principle of accuracy. More specifically, the couplet and/or is largely redundant because the word or logically and grammatically encompasses the same meaning: or is ‘inclusive’. What and/or attempts to address, is the mental paranoia that A or B could be interpreted in an ‘exclusive’ rather than an ‘inclusive’ manner: the exclusive meaning would be that A or B could be understood as A or B but not both. What using and/or actually does is making it worse.

The slash. Let’s consider the slash in “and/or”. What does “ / ” mean? Grammatically, the slash is not a punctuation sign (like the comma and semi-colon are). It is also not a letter and combining it with and and or does not create a new, compound word (none of my dictionaries mentions and/or or its translated equivalent).
In my view, the slash introduces a choice, optionality. If we write he/she it is fairly obvious that the person aimed at could be a man or a woman, or, if you happen to have it in mind, both. Like in he/she, the slash should be read to mean or: he or she or, in this case, and or or. Now reconsider the above examples: A and/or B would then read A and or or B or A and (or or) B. Whilst the case with “he/she” is fairly clear (at least unequivocally understandable); with this clarification, the meaning of and/or has become really confusing. Note that for someone favouring the use of and/or, to be consistent, he or she should convert the slash into A and and/or or B

Law or language? If a court must consider the issue, it would not be concerned (pro se) with the grammatical meaning of the words. A court’s role is to establish the meaning contracting parties have (reasonably) attributed to their contract. In establishing such meaning, it makes perfectly sense that the court relies on a dictionary or grammar book. Most of these books do not acknowledge and/or to have a distinct meaning. So a court must make something out of it. It is appropriate that this starts with the rules and fundamentals of language: grammar. In the absence of other indicators, those rules and principles should be determinative.

The ICC International Standby Practices[1] contain provisions on the use of and/or in (standby) documents:

1.10 – Redundant or otherwise undesirable terms

(b) A standby should not use the term “and/or” (if it does it means either or both).

1.11 – Interpretation of these rules

(c) Unless the context otherwise requires:

(iv)  “A or B” means “A or B or both”; “either A or B” means “A or B, but not both”; and “A and B” means “both A and B”;

Or. Typically, it is sufficient to write or, because it captures or both as well. Erroneously only and is meant.

[1]      ICC Publication N° 590, International standby practices (“ISP 98”).