The answer to that question may sound simple. The basic concept behind the term theft is relatively easy to understand, how the act can be accomplished varies greatly depending on the circumstances.
The California Penal Code describes the different methods used by thieves to achieve their goal: “Every person who shall feloniously steal, take, carry, lead, or drive away the personal property of another, or who shall fraudulently appropriate property which has been entrusted to him or her, or who shall knowingly and designedly, by any false or fraudulent representation or pretense, defraud any other person of money, labor or real or personal property, or who causes or procures others to report falsely of his or her wealth or mercantile character and by thus imposing upon any person, obtains credit and thereby fraudulently gets or obtains possession of money, or property or obtains the labor or service of another, is guilty of theft.”
Earlier versions of the law referred to different forms of theft as larceny, embezzlement, or stealing.
To simplify any confusion, “theft” has replaced larceny and the other earlier terms. Now whenever, “any law or statute of this state refers to or mentions larceny, embezzlement, or stealing, said law or statute shall hereafter be read and interpreted as if the word ‘theft’ were substituted therefor.”
While the names of various offenses have been reduced to a single term, the crimes themselves have not been altered they remain the same as they were under the older terms. When determining whether a theft crime has been committed it is necessary often to look to the elements of their previous versions for the answer.
The term Larceny applies to a theft or taking from another where the taking is not from the owner directly, but by a thief having custody of the owner’s property at the time of the taking who converts it to their own use.
The fact a person or owner of property who is no longer in actual possession of the property can be the victim of a theft or taking is a legal fiction referred to as “constructive possession.” A person, or thief may have legal or consensual “custody” of the property of the owner, in a manner that is not considered actual “possession,” since it does not involve the transfer of title and is usually only temporary. If a thief having custody under these circumstances converts the property to their own use while it is in their custody, then they have taken it from the owner’s “constructive possession.” The conversion of the owner’s property by the thief is considered taking it from the owner’s actual possession even though the owner does not have actual possession at the time of the taking. The taking element of the theft is satisfied by using a legal construct that may defy logic, but satisfies the necessary element of taking.LOST PROPERTY
The same concept applies to lost property. Even though the property is no longer in the actual possession of the owner it is nevertheless deemed to be in the constructive possession of the owner. If a person finds lost property and there is an attempt to locate the owner then there is no theft. However, if there exist facts that may identify the actual owner of the property, the finder must attempt to locate the owner, if they don’t and appropriate the property to their own use they are guilty of a larceny.
 Section 490a of the California Penal Code http://law.onecle.com/california/penal/490a.html; People v. Davis (1998) 19 C.4th 301, 304, 79 C.R.2d 295, 965 P.2d 1165 http://scocal.stanford.edu/opinion/people-v-davis-31960
 People v. Ashley (1954) 42 C.2d 246, 258, 267 P.2d 271 http://scocal.stanford.edu/opinion/people-v-ashley-24018; People v. Carter (1933) 131 C.A. 177, 183, 21 P.2d 129 https://casetext.com/case/people-v-carter-194; People v. Edwards (1933) 133 C.A. 335, 339, 24 P.2d 183 https://www.google.com/search?q=People+v.+Edwards+(1933)&oq=People+v.+Edwards+(1933)&aqs=chrome..69i57.6591j0j4&sourceid=chrome&ie=UTF-8
 People v. Davis (1893) 97 C. 194, 195,
 Section 485 of the California Penal Code http://codes.findlaw.com/ca/penal-code/pen-sect-485.html; People v. Buelna (1889) 81 C. 135, 137; Section 484 of the California Penal Code https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?sectionNum=484.&lawCode=PEN; People v. Moses (1990) 217 C.A.3d 1245, 1252, footnote 7 https://www.google.com/search?q=People+v.+Moses+(1990)&oq=People+v.+Moses+(1990)&aqs=chrome..69i57.7078j0j9&sourceid=chrome&ie=UTF-8; People v. Zamani (2010) 183 C.A.4th 854, 865, 866 http://law.justia.com/cases/california/court-of-appeal/2010/h032414/; People v. Baker (2005) 126 C.A.4th 463, https://casetext.com/case/people-v-baker-282