I'm learning about drafting a patent. I was told you should walk a line between broad and narrow. You want the claims to cover many things but not so many that they infringe prior art. So I was told the best thing to do is make the claims vague and later down the line argue that they means something. Is this a good strategy?
Whether it is good depends on your view of why you are applying for a patent. This gets a little philosophical.
The classical view is that a patent protects an invention so that an inventor can exploit it with a limited monopoly. The value of the patent is inherently linked to how it enables the owner to exploit the underlying invention, and to prevent infringement. Such a view is common for many pharmaceutical patents, where a monopoly over a drug can be worth billions.
The modern view is that a patent itself is an asset, independent of how it might link to the owner's exploitation of the underlying invention. That is, a patent has value through licensing fees, so it is useful to encourage infringement so as to enable such fees. Such a view is common for many telecommunications patents, where having a standards-essential patent can bring you licensing fees worth millions.
This neatly dovetails into how a patent application should be drafted.
If you want a patent to protect your exploitation of the invention, then it makes sense to clearly define what your invention is: protection for things other than those that affect the exploitation of your invention is unnecessary. Your description would be tightly linked to the implementation of your invention, with relatively few alternative embodiments. Your claims would not be overly broad, and would be clearly directed to the core of the invention. The chance that relevant prior art will arise will be lower, but if does turn up, it's more likely to be fatal.
If you want a patent for secondary reasons like licensing fees, then it makes sense to be cagey about what you are protecting. Your description would be full of "mays", optional embodiments, and ranges of possibilities. The claims would be very broad, to make it hard for someone else to avoid infringement. The chance that relevant prior art will arise is much higher, since your broad and vague claims will encompass a lot more, but you will have more freedom to find suitable amendments and argue around it. Moreover, the chance that you will receive clarity or sufficiency objections is much higher (particularly in stricter jurisdictions like the EPO), which may be impossible to overcome if you have been too greedy.