How to self-learn law today, like those lawyers in the past who never went to law school? One can simply read law textbooks and judgements of legal cases, but what else?
If you simply want to acquire knowledge in law, reading is the most effective way. Even law courses (at least where I am from) consists of tons and tons of reading. Read, read, read. Usually the items are: Legislation (i.e. the actual law). If you are attending an Intellectual Property class, you will be assigned to read Copyright laws. In a Criminal Law class you will read the laws about prosecution, and legal definitions of various crimes. Textbook / lecture slides. They will provide a laymen explanation of the concepts and terms you come across in the legislation, along with simple examples. Legal cases. These are especially important in a country where Common Law is in practice. Here is a fact: you cannot learn every aspect of law. There is simply too much. That is why there are lawyers who specialize in contract, accident compensation, land dispute, etc.
If you say something twice, eventually they’ll be in conflict Law codes are vast. They deal with many things and sometimes, as here, they deal with the same thing twice. If they duplicated themselves, rather than cross-referencing, every time the law was changed, every single instance would have to be tracked down and changed. Admittedly, that is not as big a problem with digital codes (but still not infallible and definitely time-consuming) but when these would have to be found by hand, it was damn near impossible. Written this way, change it once and it’s changed everywhere. My first boss taught me that. The fired was engineering rather than law but the principle is the same.
Here is a substantial collection of interpretive canons; this article discusses rules vs. canons. This article discusses contract interpretation from both the perspectives of drafting and litigating. These are all from the perspective of common law systems. This article (in English) and this chapter (English, paywall) reminds us that French contract law is different, to which I would add this which focuses on the French subjective theory of contracts – starkly distinct from the common law theory. This page (en français) will probably be of most interest to you. The 2016 modification to the civil code added art. 1190 (and other articles) which says Dans le doute, le contrat de gré à gré s'interprète contre le créancier et en faveur du débiteur, et le contrat d'adhésion contre celui qui l'a proposé which is contra proferentem. The Latin name is not officially assigned to this law, and being a new addition to French law, it's too early to tell if it will be so named in French legal practice.
In my experience, varying jurisdictions can and do differ as to the myriad ways these disputes are resolved. Contract law is one area where the judge has a lot of discretion. This is definitely true in state courts, even from judge to judge, and can even be true in the federal level-The 9th Circuit has some wildly different appellate decisions when compared to the 1st Circuit, and so on. I say this not to be argumentative, but to highlight the importance of careful and concise drafting that fully explicates the bargained for exchange, as there can be a vast amount of judicial subjectivity that goes into determining which rules pertain to certain situations. "Conflicting or competing clause" cases are now some of the most commonly litigated contract disputes. This is largely because the last 20 years has seen a huge influx of people "drafting" (more like piecing together) contracts without benefit of qualified counsel. This is particularly true because lay people do not generally create a specific insturment like an attorney would - from scratch, with definitions and terms specific to the transaction. Rather, they go online and find "form" or model contracts that they feel are close enough (which are almost always missing key components), and then they type in their own terms, or even write them in. Because this is so common, most jurisdictions follow the rule that hand written terms supersede pre-printed terms; likewise, type written terms will take precedence over pre-printed terms. Specific terms also carry more weight than general terms. Specific terms will usually be given precedence over general terms, as these are seen as creating a specific exception to the general terms. For example, if Clause A in your scenario said: Written notice must be provided at least five days in advance of (any) change... (leaving out "to price"), then clause B would prevail because it would be more specific than the more general term (A), which in my scene would pertain to any change whatsoever (this is assuming the whole of the agreement did not shed light on the issues more fully). In your hypothetical, these are both specific terms. In that case, the court would first examine the entire contract and all addendum, specs, plans, etc. when interpreting competing or conflicting clauses applying the fundamental principal that a contract should always be interpreted as a whole - not clause-by-clause - and not section-by-section. Contracts will often have numerous parts with portions incorporated specifically by reference, or numerous documents that may be integral to the transaction, If the parties agree to what constitutes the various parts of the contract (even if not incorporated) the entirety of the transactional documents may be considered by the trier of fact (and law). Once examined, if a proposed interpretation makes other portions of the global agreement meaningless, illogical or unenforceable, and another party's interpretation is in keeping with the document as a whole, that is the interpretation that will typically be adopted. Assuming this analysis doesn't work to resolve the issue, then the court would look to see if there is an order-of-precedence clause, which is a clause that lays out what parts of the contract / types of clauses take precedence over others (ex. written requirements take precendee over performance requirements, addendum hold less import than the signed agreement, schematics hold less import than addendum, and so on). Assuming this there is no order of precedence, the court will look first to see if the contract was negotiated back and forth, with terms being modified with each draft. If Yes, then the court will except extrinsic evidence (parole evidence) that goes to the intent of the parties bargained for exchange. If not, the contract term(s) will be construed against the drafter and in favor of the one who signed the others' instrument. So, as you can see, there is no clear answer to what seems to be a simple issue. This just goes to show: Lawyers seem expensive when you decide to hire them - Lawyers are expensive when you have to hire them, because you decided not to in the first place!
While it is true that jury instructions are typically less than optimal, it is ideological hyperbole or cynicism to claim that instructions are purposely confusing. The ultimate source of the confusion is that the legal system has to assume (pretend) that it has clear-cut rules that any reasonable person can easily understand and automatically apply. In order to maintain uniformity of the law, there is an externally-defined instruction that a judge may read (rather than giving his personal spin on what "reasonable doubt" means or what the relationship is between "reasonable doubt" and convicting a defendant). Once the relevant body of government (committee of judges and lawyers) has established the apparently correct formula for expressing the applicable legal concept, they don't mess with it, until SCOTUS overturns decisions enough times based on crappy instructions. Legal professionals are trained to carefully scrutinze language so as to achieve a single interpretation of a given clause (never mind the fact that there turn out to be many such interpretations). Since they can apply these interpretive rules, it is assumed that anyone can apply them. But in fact, we know that people don't just use literal semantic principles to reach conclusions – but the law resist pandering to that imperfection in human behavior. There is a huge literature on problems of jury instructions, some of the better of which relies on psycholinguistic experimentation to establish that a given instruction is confusing or gives the wrong result. See for example Solan's "Refocusing the burden of proof.." (and references therein) that addresses the problem of the "beyond a reasonable doubt" instruction, which has the unintended consequence of implying that the defense has an obligation to create a doubt (which is not the case, and allows conviction if there is the weakest imaginable evidence which hasn't been refuted). But who gets to decide what the improved instructions should say? The instructions have to correctly state what the law holds (where "the law" means not just statutes, but the trillions of relevant court decisions and applicable regulations). Thus there is massive inertia, and improved jury instructions will not come about quickly.
SCOTUS blog regularly does posts on that kind of topic (see, e.g., their Stat Pack) and if you looked at their sources or the authors of those posts, you could probably easily find more. There are people who do that and make their findings publicly available, but I don't know them off hand.
Primary Theory I suspect there might not be a legal answer to this question. I have always suspected a sort of pseudo-intellectual elitism (or simple preference or carelessness) with passive voice sentence construction in general. I sense license writers have not (yet) escaped this general trend. I would love someone to prove this theory incorrect. But, alas, I doubt it will happen. Alternative Theory But because this is a Law Q&amp;A site, I will advance the following alternative theory. I don't believe it's correct. But I will advance it because it's the only possible explanation I can think of that might be even remotely based on legal reasoning... Maybe they are just basing their construction on the way the law itself is written? For example, if the law says, "Permission must be granted..." Then it would follow that a writer who wants to comply with the law might choose, "Permission is hereby granted..." instead of something like "The authors hereby grant permission..." or, as the OP suggested, "You may..."
Why is it against the law to practice law without a license? Most, if not all, jurisdictions have decided to implement a law that requires such a licence (or similar) to ensure that practitioners are properly authorised, regulated and competent in the best interests of the administration of justice and to maintain a high standard of professionalism. Any shortcomings can then be addressed either by law or the relevant regulating body.