Final answer:
A patent may be invalid if the invention lacks novelty, is obvious, is not useful, or was filed too late. Patents typically last about 20 years, balancing inventors' earnings and preventing monopolies.
Step-by-step explanation:
A patent could be invalidated under several conditions, all of which are key to ensuring that only genuinely novel and non-obvious inventions receive legal protection. The first condition is if the invention is not novel, meaning that it already exists in the public domain and therefore cannot be claimed by someone else. Secondly, a patent may be invalid if the invention is obvious to a person with ordinary skills in the field; it must represent a non-trivial advancement. Third, a patent can be stripped if the invention is not useful, indicating that it must have a clear practical application or utility. Lastly, if the patent application was not filed within the specified time frame, it may likewise be considered invalid. The time periods for patents, which are typically around 20 years, seek a balance between providing inventors time to profit from their creations and preventing long-term monopolies.