Why are national defence and street lighting classic examples of public goods?

National defence and street lighting are classic examples of public goods because they are non-excludable and non-rivalrous.

Public goods are goods that are provided by the government or the public sector for the benefit of all members of society. They are characterised by two main features: non-excludability and non-rivalry. Non-excludability means that once the good is provided, no one can be excluded from using it. Non-rivalry means that one person's use of the good does not reduce its availability to others.

National defence is a classic example of a public good. It is non-excludable because once the government provides national defence, all citizens are protected, regardless of whether they have contributed to its provision or not. It is also non-rivalrous because one person's protection does not reduce the level of protection available to others. In other words, the protection of one citizen does not come at the expense of another. This is why national defence is typically provided by the government, as it would be difficult for a private company to exclude non-payers and to charge individuals for their personal use.

Street lighting is another classic example of a public good. It is non-excludable because once the lights are on, everyone can benefit from them, regardless of whether they have paid for them or not. It is also non-rivalrous because one person's use of the light (i.e., walking under it at night) does not reduce the light available to others. Again, this is why street lighting is typically provided by the local government, as it would be impractical for a private company to charge individuals for their personal use of the light.

In conclusion, national defence and street lighting are classic examples of public goods due to their non-excludability and non-rivalry characteristics. They are provided for the benefit of all members of society and their use by one individual does not reduce their availability to others.