# I Existence of spanning set for every vector space

1. Jan 29, 2017

### Mr Davis 97

I know that the span of any subset of vectors in a vector space is also a vector space (subspace), but is it true that every vector space has a generating set? That is, the moment that we define a vector space, does there necessarily exist a spanning set consisting of its vectors?

2. Jan 29, 2017

### Stephen Tashi

Trivially, you can take all vectors in the vector space as a spanning set. To make the question interesting, you must put more requirements on the kind of spanning set that you want.

Some textbooks declare that by the phrase "vector space", they will mean a "finite dimensional vector space". How do your course materials use the phrase "vector space"?

3. Jan 30, 2017

### pwsnafu

Are we assuming axiom of choice?

4. Jan 30, 2017

### Mr Davis 97

A vector space can be finite or infinite dimensional, and we are assuming the axiom of choice.

5. Jan 30, 2017

### Stephen Tashi

The set consisting of all vectors in the vector space spans the vector space. The question becomes more complicated if you demand a set that spans the space and has special properties. For example, if there are an uncountably infinite number of vectors in the vector space then does there exist a countably infinite set of vectors that spans the space?

6. Jan 31, 2017

### pwsnafu

The statement "every vector space has a basis" is equivalent to AC. So just use that.